[apex] Exception applying rule UnusedLocalVariable on trigger

Fixes #2554

docs/pages/release_notes.md

@@ -16,6 +16,9 @@ This is a {{ site.pmd.release_type }} release.
 
 ### Fixed Issues
 
+*   apex-bestpractices
+    *   [#2554](https://github.com/pmd/pmd/issues/2554): \[apex] Exception applying rule UnusedLocalVariable on trigger
+
 ### API Changes
 
 ### External Contributions

pmd-apex/src/main/java/net/sourceforge/pmd/lang/apex/rule/bestpractices/UnusedLocalVariableRule.java

@@ -24,6 +24,10 @@ public class UnusedLocalVariableRule extends AbstractApexRule {
         String variableName = node.getImage();
 
         ASTBlockStatement variableContext = node.getFirstParentOfType(ASTBlockStatement.class);
+        if (variableContext == null) {
+            // if there is no parent BlockStatement, e.g. in triggers
+            return data;
+        }
 
         List<ApexNode<?>> potentialUsages = new ArrayList<>();
 

pmd-apex/src/test/resources/net/sourceforge/pmd/lang/apex/rule/bestpractices/xml/UnusedLocalVariable.xml

@@ -83,6 +83,17 @@ public class Foo {
     public String fieldUsage() {
         return myfield;
     }
+}
+        ]]></code>
+    </test-code>
+
+    <test-code>
+        <description>NPE with triggers (#2554)</description>
+        <expected-problems>0</expected-problems>
+        <code><![CDATA[
+trigger leadOwnerUpdate on Lead (after update) {
+    for(Lead Id : Trigger.new) {
+    }
 }
         ]]></code>
     </test-code>