Solarium suggester return 0 result

Question

I setup suggester query in solr. I have the following setting,

Solar config

  <searchComponent name="suggest" class="solr.SuggestComponent">
    <lst name="suggester">
      <str name="name">mySuggester</str>
      <str name="lookupImpl">FuzzyLookupFactory</str>
      <str name="dictionaryImpl">DocumentDictionaryFactory</str>
      <str name="field">productSuggest</str>
      <str name="suggestAnalyzerFieldType">string</str>
    </lst>
  </searchComponent>

  <requestHandler name="/suggest" class="solr.SearchHandler" startup="lazy">
    <lst name="defaults">
      <str name="suggest">true</str>
      <str name="suggest.count">10</str>
      <str name="suggest.dictionary">mySuggester</str>
    </lst>
    <arr name="components">
      <str>suggest</str>
    </arr>
  </requestHandler>

Schema file

  <field name="SpecMaterial" type="string" uninvertible="true" default="SpecMaterial" indexed="true" stored="true"/>

  <copyField source="SpecMaterial" dest="productSuggest" maxChars="30000"/>
  <field name="productSuggest" type="textSuggest" default="productSuggest" stored="true" indexed="true"/>

  <fieldType class="solr.TextField" name="textSuggest" positionIncrementGap="100">
    <analyzer>
      <tokenizer class="solr.StandardTokenizerFactory"/>
      <filter class="solr.StandardFilterFactory"/>
      <filter class="solr.LowerCaseFilterFactory"/>
    </analyzer>
  </fieldType>

I run using this below url

   http://localhost:8983/solr/test_products/suggest?suggest=true&suggest.dictionary=mySuggester&wt=json&suggest.q=Medium

But the suggester return 0 result like,

{
  "responseHeader":{
    "status":0,
    "QTime":0},
  "suggest":{"mySuggester":{
      "Medium":{
        "numFound":0,
        "suggestions":[]}
       }
   }
}

If any mistake are there in code? And why we can use copyfeild in suggester?