diff --git a/sdk/python/feast/api/registry/rest/data_sources.py b/sdk/python/feast/api/registry/rest/data_sources.py
index 4927999a951..33200d2a534 100644
--- a/sdk/python/feast/api/registry/rest/data_sources.py
+++ b/sdk/python/feast/api/registry/rest/data_sources.py
@@ -44,7 +44,7 @@ def list_data_sources(
         data_sources = response.get("dataSources", [])
 
         result = {
-            "data_sources": data_sources,
+            "dataSources": data_sources,
             "pagination": response.get("pagination", {}),
         }
 
diff --git a/sdk/python/feast/api/registry/rest/entities.py b/sdk/python/feast/api/registry/rest/entities.py
index 318fdb5822b..3d39dfbf0f3 100644
--- a/sdk/python/feast/api/registry/rest/entities.py
+++ b/sdk/python/feast/api/registry/rest/entities.py
@@ -95,10 +95,28 @@ def get_entity(
 
         result = entity
 
+        relationships = get_object_relationships(
+            grpc_handler, "entity", name, project, allow_cache
+        )
+        ds_list_req = RegistryServer_pb2.ListDataSourcesRequest(
+            project=project,
+            allow_cache=allow_cache,
+        )
+        ds_list_resp = grpc_call(grpc_handler.ListDataSources, ds_list_req)
+        ds_map = {ds["name"]: ds for ds in ds_list_resp.get("dataSources", [])}
+        data_source_objs = []
+        seen_ds_names = set()
+        for rel in relationships:
+            if rel.get("target", {}).get("type") == "dataSource":
+                ds_name = rel["target"]["name"]
+                if ds_name not in seen_ds_names:
+                    ds_obj = ds_map.get(ds_name)
+                    if ds_obj:
+                        data_source_objs.append(ds_obj)
+                        seen_ds_names.add(ds_name)
+        result["dataSources"] = data_source_objs
+
         if include_relationships:
-            relationships = get_object_relationships(
-                grpc_handler, "entity", name, project, allow_cache
-            )
             result["relationships"] = relationships
 
         return result
diff --git a/sdk/python/feast/api/registry/rest/features.py b/sdk/python/feast/api/registry/rest/features.py
index 74a9c4bd5f3..7e6296a9858 100644
--- a/sdk/python/feast/api/registry/rest/features.py
+++ b/sdk/python/feast/api/registry/rest/features.py
@@ -39,9 +39,15 @@ def list_features(
             sorting=create_grpc_sorting_params(sorting_params),
         )
         response = grpc_call(grpc_handler.ListFeatures, req)
+        if "features" not in response:
+            response["features"] = []
+        if "pagination" not in response:
+            response["pagination"] = {}
+
         if include_relationships:
+            features = response.get("features", [])
             relationships = get_relationships_for_objects(
-                grpc_handler, response["features"], "feature", project, allow_cache
+                grpc_handler, features, "feature", project, allow_cache
             )
             response["relationships"] = relationships
         return response
diff --git a/sdk/python/tests/unit/api/test_api_rest_registry.py b/sdk/python/tests/unit/api/test_api_rest_registry.py
index 2748994ba4e..bc893861938 100644
--- a/sdk/python/tests/unit/api/test_api_rest_registry.py
+++ b/sdk/python/tests/unit/api/test_api_rest_registry.py
@@ -145,8 +145,7 @@ def test_feature_services_via_rest(fastapi_test_app):
 
 def test_data_sources_via_rest(fastapi_test_app):
     response = fastapi_test_app.get("/data_sources?project=demo_project")
-    assert response.status_code == 200
-    assert "data_sources" in response.json()
+    assert "dataSources" in response.json()
     response = fastapi_test_app.get(
         "/data_sources/user_profile_source?project=demo_project"
     )
@@ -650,9 +649,9 @@ def test_data_sources_pagination_via_rest(fastapi_test_app_with_multiple_objects
     response = client.get("/data_sources?project=demo_project&page=1&limit=2")
     assert response.status_code == 200
     data = response.json()
-    assert "data_sources" in data
+    assert "dataSources" in data
     assert "pagination" in data
-    assert len(data["data_sources"]) == 2
+    assert len(data["dataSources"]) == 2
     assert data["pagination"]["page"] == 1
     assert data["pagination"]["limit"] == 2
     assert data["pagination"]["totalCount"] == 3
@@ -669,7 +668,7 @@ def test_data_sources_sorting_via_rest(fastapi_test_app_with_multiple_objects):
     )
     assert response.status_code == 200
     data = response.json()
-    ds_names = [ds["name"] for ds in data["data_sources"]]
+    ds_names = [ds["name"] for ds in data["dataSources"]]
     assert ds_names == sorted(ds_names)
 
 
@@ -1064,3 +1063,70 @@ def test_lineage_complete_all_via_rest(fastapi_test_app):
         assert "dataSources" in project_data["objects"]
         assert "featureViews" in project_data["objects"]
         assert "featureServices" in project_data["objects"]
+
+
+def test_invalid_project_name_with_relationships_via_rest(fastapi_test_app):
+    """Test REST API response with invalid project name using include_relationships=true.
+    The API should not throw 500 or any other error when an invalid project name is provided
+    with include_relationships=true parameter.
+    """
+    response = fastapi_test_app.get(
+        "/entities?project=invalid_project_name&include_relationships=true"
+    )
+    assert response.status_code == 200
+    data = response.json()
+    assert "entities" in data
+    assert isinstance(data["entities"], list)
+    assert len(data["entities"]) == 0
+    assert "relationships" in data
+    assert isinstance(data["relationships"], dict)
+    assert len(data["relationships"]) == 0
+
+    response = fastapi_test_app.get(
+        "/feature_views?project=invalid_project_name&include_relationships=true"
+    )
+    assert response.status_code == 200
+    data = response.json()
+    assert "featureViews" in data
+    assert isinstance(data["featureViews"], list)
+    assert len(data["featureViews"]) == 0
+    assert "relationships" in data
+    assert isinstance(data["relationships"], dict)
+    assert len(data["relationships"]) == 0
+
+    response = fastapi_test_app.get(
+        "/data_sources?project=invalid_project_name&include_relationships=true"
+    )
+    # Should return 200 with empty results, not 500 or other errors
+    assert response.status_code == 200
+    data = response.json()
+    assert "dataSources" in data
+    assert isinstance(data["dataSources"], list)
+    assert len(data["dataSources"]) == 0
+    assert "relationships" in data
+    assert isinstance(data["relationships"], dict)
+    assert len(data["relationships"]) == 0
+
+    response = fastapi_test_app.get(
+        "/feature_services?project=invalid_project_name&include_relationships=true"
+    )
+    assert response.status_code == 200
+    data = response.json()
+    assert "featureServices" in data
+    assert isinstance(data["featureServices"], list)
+    assert len(data["featureServices"]) == 0
+    assert "relationships" in data
+    assert isinstance(data["relationships"], dict)
+    assert len(data["relationships"]) == 0
+
+    response = fastapi_test_app.get(
+        "/features?project=invalid_project_name&include_relationships=true"
+    )
+    assert response.status_code == 200
+    data = response.json()
+    assert "features" in data
+    assert isinstance(data["features"], list)
+    assert len(data["features"]) == 0
+    assert "relationships" in data
+    assert isinstance(data["relationships"], dict)
+    assert len(data["relationships"]) == 0