NIFI-6127: Fixed NPE in match() and find() EL functions when attribute doesn't exist

This closes #3378.

Signed-off-by: Koji Kawamura <ijokarumawak@apache.org>

nifi-commons/nifi-expression-language/src/main/java/org/apache/nifi/attribute/expression/language/evaluation/functions/FindEvaluator.java

@@ -53,7 +53,11 @@ public class FindEvaluator extends BooleanEvaluator {
         }
         final Pattern pattern;
         if (compiledPattern == null) {
-            pattern = Pattern.compile(search.evaluate(attributes).getValue());
+            String expression = search.evaluate(attributes).getValue();
+            if (expression == null) {
+                return new BooleanQueryResult(false);
+            }
+            pattern = Pattern.compile(expression);
         } else {
             pattern = compiledPattern;
         }

nifi-commons/nifi-expression-language/src/main/java/org/apache/nifi/attribute/expression/language/evaluation/functions/MatchesEvaluator.java

@@ -53,7 +53,11 @@ public class MatchesEvaluator extends BooleanEvaluator {
         }
         final Pattern pattern;
         if (compiledPattern == null) {
-            pattern = Pattern.compile(search.evaluate(attributes).getValue());
+            String expression = search.evaluate(attributes).getValue();
+            if (expression == null) {
+                return new BooleanQueryResult(false);
+            }
+            pattern = Pattern.compile(expression);
         } else {
             pattern = compiledPattern;
         }

nifi-commons/nifi-expression-language/src/test/java/org/apache/nifi/attribute/expression/language/TestQuery.java

@@ -1324,6 +1324,9 @@ public class TestQuery {
         assertEquals("false", secondEvaluation);
 
         verifyEquals("${dotted:matches('abc\\.xyz')}", attributes, true);
+
+        // Test for matches(null)
+        assertEquals("false", Query.evaluateExpressions("${abc:matches(${not.here})}", attributes, null));
     }
 
     @Test
@@ -1344,6 +1347,9 @@ public class TestQuery {
         assertEquals("false", secondEvaluation);
 
         verifyEquals("${dotted:find('\\.')}", attributes, true);
+
+        // Test for find(null)
+        assertEquals("false", Query.evaluateExpressions("${abc:find(${not.here})}", attributes, null));
     }
 
     @Test