[core] Can not set ruleset property value to empty

[hgschmie]

Affects PMD Version:

6.53.0

Description:

Docs claim "Test class name pattern to identify test classes by their fully qualified name. An empty pattern disables test class detection by name. Since PMD 6.51.0."

However, adding this to my custom pmd config:

<rule ref="category/java/errorprone.xml/TestClassWithoutTestCases">
        <properties>
            <property name="testClassPattern" value="" />
        </properties>
    </rule>

leads to

Exception Stacktrace:

Caused by: java.lang.NullPointerException: Cannot invoke "String.isEmpty()" because "this.pattern" is null
    at java.util.regex.Pattern.<init> (Pattern.java:1428)
    at java.util.regex.Pattern.compile (Pattern.java:1069)
    at net.sourceforge.pmd.properties.ValueParserConstants$10.valueOf (ValueParserConstants.java:211)
    at net.sourceforge.pmd.properties.ValueParserConstants$10.valueOf (ValueParserConstants.java:208)
    at net.sourceforge.pmd.properties.GenericPropertyDescriptor.createFrom (GenericPropertyDescriptor.java:68)
    at net.sourceforge.pmd.properties.AbstractSingleValueProperty.valueFrom (AbstractSingleValueProperty.java:129)
    at net.sourceforge.pmd.rules.RuleFactory.setRulePropertyCapture (RuleFactory.java:307)
    at net.sourceforge.pmd.rules.RuleFactory.setPropertyValues (RuleFactory.java:302)
    at net.sourceforge.pmd.rules.RuleFactory.decorateRule (RuleFactory.java:126)
    at net.sourceforge.pmd.RuleSetFactory.parseRuleReferenceNode (RuleSetFactory.java:726)
    at net.sourceforge.pmd.RuleSetFactory.parseRuleNode (RuleSetFactory.java:505)
    at net.sourceforge.pmd.RuleSetFactory.parseRuleSetNode (RuleSetFactory.java:409)
    at net.sourceforge.pmd.RuleSetFactory.createRuleSet (RuleSetFactory.java:234)
    at net.sourceforge.pmd.RuleSetFactory.createRuleSet (RuleSetFactory.java:229)
    at net.sourceforge.pmd.RuleSetLoader.loadFromResource (RuleSetLoader.java:253)
    at net.sourceforge.pmd.RuleSetLoader.loadFromResource (RuleSetLoader.java:153)
    at net.sourceforge.pmd.RuleSetLoader.loadFromResources (RuleSetLoader.java:185)
    at org.apache.maven.plugins.pmd.exec.PmdExecutor.processFilesWithPMD (PmdExecutor.java:351)
    at org.apache.maven.plugins.pmd.exec.PmdExecutor.run (PmdExecutor.java:248)
    at org.apache.maven.plugins.pmd.exec.PmdExecutor.execute (PmdExecutor.java:83)
    at org.apache.maven.plugins.pmd.PmdReport.executePmd (PmdReport.java:390)
    at org.apache.maven.plugins.pmd.PmdReport.canGenerateReport (PmdReport.java:315)

Code Sample demonstrating the issue:

not needed.

Steps to reproduce:

Please provide detailed steps for how we can reproduce the bug.

1. add example above to custom ruleset.
2. run pmd with the ruleset
3. profit

Running PMD through: [Maven]