diff --git a/rest-api-spec/src/main/resources/rest-api-spec/test/index/91_flat_object_null_value.yml b/rest-api-spec/src/main/resources/rest-api-spec/test/index/91_flat_object_null_value.yml
index 98abd58a54e4b..716b6fb51cb43 100644
--- a/rest-api-spec/src/main/resources/rest-api-spec/test/index/91_flat_object_null_value.yml
+++ b/rest-api-spec/src/main/resources/rest-api-spec/test/index/91_flat_object_null_value.yml
@@ -16,12 +16,15 @@ setup:
             properties:
               record:
                 type: "flat_object"
+              order:
+                type: "integer"
   - do:
       index:
         index: flat_object_null_value
         id: 1
         body: {
-          "record": null
+          "record": null,
+          "order" : 1
         }
 
   - do:
@@ -31,7 +34,8 @@ setup:
         body: {
           "record": {
             "name": null
-          }
+          },
+          "order" : 2
         }
 
   - do:
@@ -43,7 +47,8 @@ setup:
             "name": null,
             "age":"5",
             "name1": null
-          }
+          },
+          "order" : 3
         }
 
   - do:
@@ -60,7 +65,8 @@ setup:
                 }
               }
             ]
-          }
+          },
+          "order" : 4
         }
 
   - do:
@@ -77,7 +83,8 @@ setup:
               },
               null
             ]
-          }
+          },
+          "order" : 5
         }
 
   - do:
@@ -97,7 +104,8 @@ setup:
                 }
               }
             ]
-          }
+          },
+          "order" : 6
         }
 
   - do:
@@ -108,7 +116,8 @@ setup:
           "record": {
             "name": null,
             "age":"3"
-          }
+          },
+          "order" : 7
         }
 
   - do:
@@ -119,7 +128,8 @@ setup:
           "record": {
             "age":"3",
             "name": null
-          }
+          },
+          "order" : 8
         }
 
   - do:
@@ -133,7 +143,8 @@ setup:
               3
             ],
             "age": 4
-          }
+          },
+          "order" : 9
         }
 
   - do:
@@ -147,7 +158,8 @@ setup:
               null,
               3
             ]
-          }
+          },
+          "order" : 10
         }
 
   - do:
@@ -157,7 +169,8 @@ setup:
         body: {
           "record": {
             "name": null
-          }
+          },
+          "order": 11
         }
 
   - do:
@@ -171,7 +184,8 @@ setup:
                 null
               ]
             }
-          }
+          },
+          "order": 12
         }
 
   - do:
@@ -183,7 +197,8 @@ setup:
             "labels": [
               null
             ]
-          }
+          },
+          "order": 13
         }
 
   - do:
@@ -198,7 +213,8 @@ setup:
                 null
               ]
             }
-          }
+          },
+          "order": 14
         }
 
   - do:
@@ -211,7 +227,8 @@ setup:
             "labels": [
               null
             ]
-          }
+          },
+          "order": 15
         }
 
   - do:
@@ -224,7 +241,8 @@ setup:
               null
             ],
             "age": "4"
-          }
+          },
+          "order": 16
         }
 
   - do:
@@ -239,7 +257,8 @@ setup:
                 "dsdsdsd"
               ]
             }
-          }
+          },
+          "order": 17
         }
 
   - do:
@@ -253,7 +272,8 @@ setup:
                 "name2": null
               }
             }
-          }
+          },
+          "order": 18
         }
 
   - do:
@@ -271,7 +291,8 @@ setup:
                 ]
               ]
             }
-          }
+          },
+          "order": 19
         }
 
   - do:
@@ -299,7 +320,7 @@ teardown:
   - is_true: flat_object_null_value.mappings
   - match: { flat_object_null_value.mappings.properties.record.type: flat_object }
   # https://github.com/opensearch-project/OpenSearch/tree/main/rest-api-spec/src/main/resources/rest-api-spec/test#length
-  - length: { flat_object_null_value.mappings.properties: 1 }
+  - length: { flat_object_null_value.mappings.properties: 2 }
 
 
 ---
@@ -328,7 +349,8 @@ teardown:
           size: 30,
           query: {
             exists: { "field": "record" }
-          }
+          },
+          sort: [{ order: asc}]
         }
 
   - length: { hits.hits: 12 }
@@ -352,7 +374,8 @@ teardown:
           _source: true,
           query: {
             exists: { "field": "record.d" }
-          }
+          },
+          sort: [{ order: asc}]
         }
 
   - length: { hits.hits: 3 }
@@ -367,7 +390,8 @@ teardown:
           _source: true,
           query: {
             term: { record: "dsdsdsd" }
-          }
+          },
+          sort: [{ order: asc}]
         }
 
   - length: { hits.hits: 2 }
@@ -381,7 +405,8 @@ teardown:
           _source: true,
           query: {
             term: { record.name.name1: "dsdsdsd" }
-          }
+          },
+          sort: [{ order: asc}]
         }
 
   - length: { hits.hits: 2 }
diff --git a/test/framework/src/main/java/org/opensearch/test/NotEqualMessageBuilder.java b/test/framework/src/main/java/org/opensearch/test/NotEqualMessageBuilder.java
index a70e3f15a4bf5..9524b76f255a6 100644
--- a/test/framework/src/main/java/org/opensearch/test/NotEqualMessageBuilder.java
+++ b/test/framework/src/main/java/org/opensearch/test/NotEqualMessageBuilder.java
@@ -181,18 +181,9 @@ public void compare(String field, boolean hadKey, @Nullable Object actual, Objec
             field(field, "same [" + expected + "]");
             return;
         }
-        field(
-            field,
-            "expected "
-                + expected.getClass().getSimpleName()
-                + " ["
-                + expected
-                + "] but was "
-                + actual.getClass().getSimpleName()
-                + " ["
-                + actual
-                + "]"
-        );
+        String expectedClass = expected == null ? "null object" : expected.getClass().getSimpleName();
+        String actualClass = actual == null ? "null object" : actual.getClass().getSimpleName();
+        field(field, "expected " + expectedClass + " [" + expected + "] but was " + actualClass + " [" + actual + "]");
     }
 
     private void indent() {