Added explicit 'null' check for response listener to prevent obscure NullPointerException issues (#3048)

Signed-off-by: Andriy Redko <andriy.redko@aiven.io>

client/rest-high-level/src/main/java/org/opensearch/client/RestHighLevelClient.java

@@ -1917,6 +1917,10 @@ public class RestHighLevelClient implements Closeable {
         ActionListener<Resp> listener,
         Set<Integer> ignores
     ) {
+        if (listener == null) {
+            throw new IllegalArgumentException("The listener is required and cannot be null");
+        }
+
         Request req;
         try {
             req = requestConverter.apply(request);

client/rest-high-level/src/test/java/org/opensearch/client/RestHighLevelClientTests.java

@@ -284,6 +284,20 @@ public class RestHighLevelClientTests extends OpenSearchTestCase {
         }
     }
 
+    public void testNullableActionListener() {
+        ActionRequest request = new ActionRequest() {
+            @Override
+            public ActionRequestValidationException validate() {
+                return null;
+            }
+        };
+
+        assertThrows(
+            IllegalArgumentException.class,
+            () -> restHighLevelClient.performRequestAsync(request, null, RequestOptions.DEFAULT, null, null, null)
+        );
+    }
+
     public void testParseEntity() throws IOException {
         {
             IllegalStateException ise = expectThrows(IllegalStateException.class, () -> restHighLevelClient.parseEntity(null, null));