With --auto-gen-config invalid rule references might be generated

[adangel]

See pmd/pmd#4971 for an example:

The changeset contains a change to file pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/codestyle/AbstractNamingConventionRule.java, which is not a rule by itself but a base class.

The regression tester however generates a ruleset like that:

[ERROR] Error at target/reports/HEAD/checkstyle/config.xml:8:5
  6|     <rule ref="category/apex/design.xml/CognitiveComplexity"/>
  7|     <rule ref="category/apex/design.xml/CyclomaticComplexity"/>
  8|     <rule ref="category/java/codestyle.xml/AbstractNamingConvention"/>
         ^^^^^ Unable to find referenced rule AbstractNamingConvention; perhaps the rule name is misspelled?

  9|     <rule ref="category/java/codestyle.xml/FieldNamingConventions"/>
 10|     <rule ref="category/java/codestyle.xml/IdenticalCatchBranches"/>
[ERROR] Cannot load ruleset target/reports/HEAD/checkstyle/config.xml: An XML validation error occurred

But a rule "AbstractNamingConvention" doesn't exist...

The result is, that PMD is not executed at all and the diff report shows, that all violations are missing.