diff --git a/rasa_core/nlg/callback.py b/rasa_core/nlg/callback.py
index 75083b3f9c3..99fdf05ad5e 100644
--- a/rasa_core/nlg/callback.py
+++ b/rasa_core/nlg/callback.py
@@ -25,18 +25,18 @@ def nlg_response_format_spec():
                 "type": "string"
             },
             "buttons": {
-                "type": "array",
+                "type": ["array", "null"],
                 "items": {"type": "object"}
             },
             "elements": {
-                "type": "array",
+                "type": ["array", "null"],
                 "items": {"type": "object"}
             },
             "attachment": {
-                "type": "object"
+                "type": ["object", "null"]
             },
             "image": {
-                "type": "string"
+                "type": ["string", "null"]
             }
         },
     }
diff --git a/tests/test_nlg.py b/tests/test_nlg.py
index 6cea48b77b7..b40a8bac9ae 100644
--- a/tests/test_nlg.py
+++ b/tests/test_nlg.py
@@ -79,3 +79,8 @@ def test_nlg_schema_validation():
 def test_nlg_schema_validation_empty_buttons():
     content = {"text": "Hey there!", "buttons": []}
     assert CallbackNaturalLanguageGenerator.validate_response(content)
+
+
+def test_nlg_schema_validation_empty_image():
+    content = {"text": "Hey there!", "image": None}
+    assert CallbackNaturalLanguageGenerator.validate_response(content)