JPA WrongArgumentException: SQL String cannot be NULL: despite CrudRepository save function recieving populated entity

Question

I'm making a Spring Boot (2.1.9) api, and am using Postman to POST some JSON to a function in my controller which converts it to an entity (Author). My controller object receives the object and its fields correctly, passes it to my service object and passes it to my data access object.

The problem occurs when calling the CrudRepository save(S entity) function, despite printing the fields, and verifying they aren't null, I get an exception claiming my field is indeed null. The entity is not added to the database.

I've tried adding auto_increment, changing the generationType. I've tried sending null for the Id in Postman, I've tried not sending an Id in Postman. I'm not sure what to do to fix this, since removing the @GeneratedValue seems to work, but isn't ideal since the save() would overwrite any pre-existing row with the same id with the new data as per this post.

(Note: I havent done any proper http statuses, i want to just get it working before that point)

My Controller:

@RestController
@RequestMapping(value = "/lms/admin*")
public class AdminController
{
    @Autowired
    AdminService admin;

    @PostMapping(path = "/author", produces = "application/json", consumes="application/json")
    public ResponseEntity<?> createAuthor(@RequestBody Author author) 
    {
        return new ResponseEntity<>(admin.createAuthor(author),HttpStatus.OK);
    }
    /*other CRUD operations*/
}

My Service :

@Component
public class AdminService
{
    @Autowired
    private AuthorDataAccess authorDao;

    public Author createAuthor(Author author)
    {
        System.out.println(author.toString());
        return authorDao.save(author);
    }
    /*other service functions*/
}

My Author Data Access

@Component
public interface AuthorDataAccess extends CrudRepository<Author, Integer>
{

}

My Author Entity:

@Entity 
@Table(name = "tbl_author", schema = "library")
public class Author implements Serializable
{
    private static final long serialVersionUID = 3002288345129007776L;

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE)
    @Column(updatable = false)
    private Integer authorId;
    private String authorName;

    public Author(){}


    public Author(String authorName)
    {
        this.authorName = authorName;
    }

    public Author(Integer authorId, String authorName)
    {
        this.authorId = authorId;
        this.authorName = authorName;
    }
    /*hashcode, equals, toString, getters, setters*/
}

The mySQL Table:

CREATE TABLE IF NOT EXISTS `library`.`tbl_author` (
  `authorId` INT(11) NOT NULL,
  `authorName` VARCHAR(45) NOT NULL,
  PRIMARY KEY (`authorId`))
ENGINE = InnoDB
DEFAULT CHARACTER SET = latin1;

My application.properties:

server.port=8100
spring.datasource.url=jdbc:mysql://localhost:3306/library
spring.datasource.username=root
spring.datasource.password=root
spring.application.name=admin
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.MySQL5Dialect
spring.jpa.hibernate.naming.physical-strategy=org.hibernate.boot.model.naming.PhysicalNamingStrategyStandardImpl
spring.jpa.hibernate.use-new-id-generator-mappings= false

Lastly, my pom.xml:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.9.RELEASE</version>
        <relativePath /> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.ss</groupId>
    <artifactId>lms</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>lms</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>

        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.17</version>
        </dependency>

    </dependencies>

    <build>
        <plugins>

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
                <version>2.19.1</version>
            </plugin>

            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>

        </plugins>
    </build>

</project>

Here is the exact error message i see once I've ran: mvn clean package and java -jar ./taget/<something>.jar

2019-10-13 15:37:22.037  WARN 24581 --- [nio-8100-exec-1] o.h.engine.jdbc.spi.SqlExceptionHelper   : SQL Error: 0, SQLState: S1009
2019-10-13 15:37:22.037 ERROR 24581 --- [nio-8100-exec-1] o.h.engine.jdbc.spi.SqlExceptionHelper   : SQL String cannot be NULL
2019-10-13 15:37:22.073 ERROR 24581 --- [nio-8100-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.orm.jpa.JpaSystemException: could not prepare statement; nested exception is org.hibernate.exception.GenericJDBCException: could not prepare statement] with root cause

com.mysql.cj.exceptions.WrongArgumentException: SQL String cannot be NULL
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_222]
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:1.8.0_222]
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.8.0_222]
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423) ~[na:1.8.0_222]
    at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:61) ~[mysql-connector-java-8.0.17.jar!/:8.0.17]
    at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:85) ~[mysql-connector-java-8.0.17.jar!/:8.0.17]
    at com.mysql.cj.AbstractPreparedQuery.checkNullOrEmptyQuery(AbstractPreparedQuery.java:159) ~[mysql-connector-java-8.0.17.jar!/:8.0.17]
    at com.mysql.cj.jdbc.ClientPreparedStatement.<init>(ClientPreparedStatement.java:215) ~[mysql-connector-java-8.0.17.jar!/:8.0.17]
    at com.mysql.cj.jdbc.ClientPreparedStatement.<init>(ClientPreparedStatement.java:193) ~[mysql-connector-java-8.0.17.jar!/:8.0.17]
    at com.mysql.cj.jdbc.ClientPreparedStatement.getInstance(ClientPreparedStatement.java:134) ~[mysql-connector-java-8.0.17.jar!/:8.0.17]
    at com.mysql.cj.jdbc.ConnectionImpl.clientPrepareStatement(ConnectionImpl.java:669) ~[mysql-connector-java-8.0.17.jar!/:8.0.17]
    at com.mysql.cj.jdbc.ConnectionImpl.prepareStatement(ConnectionImpl.java:1653) ~[mysql-connector-java-8.0.17.jar!/:8.0.17]
    at com.mysql.cj.jdbc.ConnectionImpl.prepareStatement(ConnectionImpl.java:1573) ~[mysql-connector-java-8.0.17.jar!/:8.0.17]
    at com.zaxxer.hikari.pool.ProxyConnection.prepareStatement(ProxyConnection.java:311) ~[HikariCP-3.2.0.jar!/:na]
    at com.zaxxer.hikari.pool.HikariProxyConnection.prepareStatement(HikariProxyConnection.java) ~[HikariCP-3.2.0.jar!/:na]
    at org.hibernate.engine.jdbc.internal.StatementPreparerImpl$1.doPrepare(StatementPreparerImpl.java:90) ~[hibernate-core-5.3.12.Final.jar!/:5.3.12.Final]
    at org.hibernate.engine.jdbc.internal.StatementPreparerImpl$StatementPreparationTemplate.prepareStatement(StatementPreparerImpl.java:176) ~[hibernate-core-5.3.12.Final.jar!/:5.3.12.Final]
    at org.hibernate.engine.jdbc.internal.StatementPreparerImpl.prepareStatement(StatementPreparerImpl.java:75) ~[hibernate-core-5.3.12.Final.jar!/:5.3.12.Final]
    at org.hibernate.id.SequenceGenerator.generateHolder(SequenceGenerator.java:114) ~[hibernate-core-5.3.12.Final.jar!/:5.3.12.Final]
    at org.hibernate.id.SequenceHiLoGenerator$1.getNextValue(SequenceHiLoGenerator.java:71) ~[hibernate-core-5.3.12.Final.jar!/:5.3.12.Final]
    at org.hibernate.id.enhanced.LegacyHiLoAlgorithmOptimizer.generate(LegacyHiLoAlgorithmOptimizer.java:60) ~[hibernate-core-5.3.12.Final.jar!/:5.3.12.Final]
    at org.hibernate.id.SequenceHiLoGenerator.generate(SequenceHiLoGenerator.java:67) ~[hibernate-core-5.3.12.Final.jar!/:5.3.12.Final]
    at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:119) ~[hibernate-core-5.3.12.Final.jar!/:5.3.12.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:192) ~[hibernate-core-5.3.12.Final.jar!/:5.3.12.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:135) ~[hibernate-core-5.3.12.Final.jar!/:5.3.12.Final]
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:62) ~[hibernate-core-5.3.12.Final.jar!/:5.3.12.Final]
    at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:804) ~[hibernate-core-5.3.12.Final.jar!/:5.3.12.Final]
    at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:789) ~[hibernate-core-5.3.12.Final.jar!/:5.3.12.Final]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_222]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_222]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_222]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_222]
    at org.springframework.orm.jpa.ExtendedEntityManagerCreator$ExtendedEntityManagerInvocationHandler.invoke(ExtendedEntityManagerCreator.java:351) ~[spring-orm-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at com.sun.proxy.$Proxy83.persist(Unknown Source) ~[na:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_222]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_222]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_222]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_222]
    at org.springframework.orm.jpa.SharedEntityManagerCreator$SharedEntityManagerInvocationHandler.invoke(SharedEntityManagerCreator.java:310) ~[spring-orm-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at com.sun.proxy.$Proxy83.persist(Unknown Source) ~[na:na]
    at org.springframework.data.jpa.repository.support.SimpleJpaRepository.save(SimpleJpaRepository.java:535) ~[spring-data-jpa-2.1.11.RELEASE.jar!/:2.1.11.RELEASE]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_222]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_222]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_222]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_222]
    at org.springframework.data.repository.core.support.RepositoryComposition$RepositoryFragments.invoke(RepositoryComposition.java:359) ~[spring-data-commons-2.1.11.RELEASE.jar!/:2.1.11.RELEASE]
    at org.springframework.data.repository.core.support.RepositoryComposition.invoke(RepositoryComposition.java:200) ~[spring-data-commons-2.1.11.RELEASE.jar!/:2.1.11.RELEASE]
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$ImplementationMethodExecutionInterceptor.invoke(RepositoryFactorySupport.java:644) ~[spring-data-commons-2.1.11.RELEASE.jar!/:2.1.11.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.doInvoke(RepositoryFactorySupport.java:608) ~[spring-data-commons-2.1.11.RELEASE.jar!/:2.1.11.RELEASE]
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.lambda$invoke$3(RepositoryFactorySupport.java:595) ~[spring-data-commons-2.1.11.RELEASE.jar!/:2.1.11.RELEASE]
    at org.springframework.data.repository.core.support.RepositoryFactorySupport$QueryExecutorMethodInterceptor.invoke(RepositoryFactorySupport.java:595) ~[spring-data-commons-2.1.11.RELEASE.jar!/:2.1.11.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.data.projection.DefaultMethodInvokingMethodInterceptor.invoke(DefaultMethodInvokingMethodInterceptor.java:59) ~[spring-data-commons-2.1.11.RELEASE.jar!/:2.1.11.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:295) ~[spring-tx-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:98) ~[spring-tx-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:139) ~[spring-tx-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$CrudMethodMetadataPopulatingMethodInterceptor.invoke(CrudMethodMetadataPostProcessor.java:144) ~[spring-data-jpa-2.1.11.RELEASE.jar!/:2.1.11.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.data.jpa.repository.support.CrudMethodMetadataPostProcessor$ExposeRepositoryInvocationInterceptor.invoke(CrudMethodMetadataPostProcessor.java:364) ~[spring-data-jpa-2.1.11.RELEASE.jar!/:2.1.11.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:93) ~[spring-aop-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.data.repository.core.support.SurroundingTransactionDetectorMethodInterceptor.invoke(SurroundingTransactionDetectorMethodInterceptor.java:61) ~[spring-data-commons-2.1.11.RELEASE.jar!/:2.1.11.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:212) ~[spring-aop-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at com.sun.proxy.$Proxy85.save(Unknown Source) ~[na:na]
    at com.ss.lms.service.AdminService.createAuthor(AdminService.java:48) ~[classes!/:0.0.1-SNAPSHOT]
    at com.ss.lms.controller.AdminController.createAuthor(AdminController.java:54) ~[classes!/:0.0.1-SNAPSHOT]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_222]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_222]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_222]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_222]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) ~[spring-web-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:105) ~[spring-webmvc-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:893) ~[spring-webmvc-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:798) ~[spring-webmvc-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040) ~[spring-webmvc-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943) ~[spring-webmvc-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:909) ~[spring-webmvc-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:660) ~[tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.26.jar!/:9.0.26]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:94) ~[spring-web-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.1.10.RELEASE.jar!/:5.1.10.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:526) [tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) [tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) [tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408) [tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:860) [tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1589) [tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_222]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_222]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.26.jar!/:9.0.26]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_222]

UPDATE

sending the controller an author with an id that doesnt already exist, still doesnt work, here is the sql:

Author [authorId=4, authorName=myName]
Hibernate: select author0_.authorId as authorId1_0_0_, author0_.authorName as authorNa2_0_0_ from tbl_author author0_ where author0_.authorId=?
Hibernate: null

SOLVED

I solved my problem by using:

@GeneratedValue(strategy = GenerationType.IDENTITY)

and using the auto_incrememnt constraint. Although to my understanding, this isn't ideal because to get the ID of the created entity, it requires the table to be traversed again. If anybody knows how to avoid this, please let me know!

Answer 1

the database existed before I started creating the api

For strategy = GenerationType.SEQUENCE to work, a db sequence must exist that can be used for the authorId column. Also, you need to specify its name using the @SequenceGenerator annotation so that JPA knows how to find it:

@GeneratedValue(generator = "authorIdGenerator", strategy = GenerationType.SEQUENCE)
@SequenceGenerator(name = "authorIdGenerator", sequenceName = <existing_sequence_name_in_the_db>, allocationSize=<correct_allocation_size_for_the_sequence>)

to get the ID of the created entity, it requires the table to be traversed again

In order to get the ID, Hibernate needs to flush the changes to the DB, because it is the DB that generates the IDs. If you use JpaRepository instead of CrudRepository as the base interface, you'll be able to call saveAndFlush instead and read the generated ID.