How do I implement Solr Deduplication? Signatures are returning 0000000000000000

Question

I'm trying to implement deduplication in Solr by updating solrconfig.xml and schema.xml according to this link: https://lucene.apache.org/solr/guide/7_6/de-duplication.html

The deduplication generates file signatures but the signatures are being set to 0000000000000000 (16 zeros). I see this other post asking the same question but no one answered it: Solr Deduplication (dedupe) giving all zeros in signatureField

Notes:

• Version: Solr 7.6.0

• I updated many of the solr.processor.* classes to solr.update.processor.* after looking at the package names in the source code: https://github.com/apache/lucene-solr/tree/branch_7_6/solr/core/src/java/org/apache/solr/update/processor

My file setup:

solrconfig.xml:

<updateRequestProcessorChain name="dedupe">
  <processor class="solr.update.processor.SignatureUpdateProcessorFactory">
    <bool name="enabled">true</bool>
    <str name="signatureField">signature</str>
    <bool name="overwriteDupes">true</bool>
    <str name="fields">name,content</str>
    <str name="signatureClass">solr.update.processor.Lookup3Signature</str>
  </processor>
  <processor class="solr.update.LogUpdateProcessorFactory" />
  <processor class="solr.update.RunUpdateProcessorFactory" />
</updateRequestProcessorChain>


<requestHandler name="/update" class="solr.UpdateRequestHandler" >
  <lst name="defaults">
    <str name="update.chain">dedupe</str>
  </lst>
</requestHandler>

schema.xml:

<field name="signature" type="string" stored="true" indexed="true" multiValued="false" />

Any help is appreciated! :)