Fix OperationResultRepoSearchAsserter

This fixes failing TestSecurityBasic.

repo/repo-test-util/src/main/java/com/evolveum/midpoint/test/asserter/OperationResultRepoSearchAsserter.java

@@ -99,7 +99,7 @@ private Predicate<OperationResult> createQuerySubstringPredicate(String expected
             @Override
             public boolean test(OperationResult operationResult) {
                 String queryParam = operationResult.getParamSingle(OperationResult.PARAM_QUERY);
-                return queryParam.contains(expectedSubstring);
+                return queryParam != null && queryParam.contains(expectedSubstring);
             }
 
             @Override