Merge branch 'pmd6-improve-pmd-analysis' into pmd7-merge-master

pmd-core/src/main/java/net/sourceforge/pmd/PMDConfiguration.java

@@ -405,9 +405,9 @@ public class PMDConfiguration extends AbstractConfiguration {
     @DeprecatedUntil700
     public void setRuleSets(@Nullable String ruleSets) {
         if (ruleSets == null) {
-            this.ruleSets.clear();
+            this.ruleSets= new ArrayList<>();
         } else {
-            this.ruleSets = Arrays.asList(ruleSets.split(","));
+            this.ruleSets = new ArrayList<>(Arrays.asList(ruleSets.split(",")));
         }
     }
 

pmd-core/src/test/java/net/sourceforge/pmd/PmdConfigurationTest.java

@@ -136,6 +136,9 @@ public class PmdConfigurationTest {
         assertEquals(listOf("/rulesets/basic.xml", "foo.xml"), configuration.getRuleSetPaths());
         configuration.setRuleSets(Collections.<String>emptyList());
         assertThat(configuration.getRuleSetPaths(), empty());
+        // should be addable even though we set it to an unmodifiable empty list
+        configuration.addRuleSet("foo.xml");
+        assertEquals(listOf("foo.xml"), configuration.getRuleSetPaths());
     }
 
     @Test