diff --git a/server/controller/workflow.py b/server/controller/workflow.py
index 77237c9..2e03e99 100644
--- a/server/controller/workflow.py
+++ b/server/controller/workflow.py
@@ -1,4 +1,4 @@
-from model.workflows import *
+from model.workflows import WorkFlowModel
 from flask import request, make_response, Blueprint
 import defusedxml.ElementTree as ET
 
@@ -6,6 +6,13 @@
 workFlowModel = WorkFlowModel()
 
 
+def isMissingWorkflow(graphml):
+    if graphml is None:
+        return True
+    # Backward-compatible guard for legacy model return type.
+    return isinstance(graphml, tuple) and len(graphml) > 0 and graphml[0] is False
+
+
 def getLasteshActionHash(root):
     xmlns = root.tag[root.tag.index('{')+1:root.tag.rindex('}')]
     return root.find(f'{{{xmlns}}}graph')\
@@ -32,7 +39,7 @@ def postWorkflow():
 @workFlow.route("/<serverID>")
 def getWorkflow(serverID):
     graphml = workFlowModel.get(serverID)
-    if graphml is None:
+    if isMissingWorkflow(graphml):
         return "Not Found", 404
     if('X-Latest-Hash' in request.headers):
         latestHash = request.headers['X-Latest-Hash']
diff --git a/server/model/workflows.py b/server/model/workflows.py
index de31434..bfff7f0 100644
--- a/server/model/workflows.py
+++ b/server/model/workflows.py
@@ -32,7 +32,7 @@ def insert(self, graphml, latestHash):
     def get(self, serverID):
         cl = self.collection.find_one({'serverID': serverID})
         if not cl:
-            return False, 'Record Not Found'
+            return None
         return cl['graphml']
 
     def update(self, serverID, graphml, latestHash, allHash):
diff --git a/server/tests/test_workflow_controller.py b/server/tests/test_workflow_controller.py
new file mode 100644
index 0000000..4966d60
--- /dev/null
+++ b/server/tests/test_workflow_controller.py
@@ -0,0 +1,82 @@
+import importlib
+import pathlib
+import sys
+import types
+import unittest
+
+from flask import Flask
+
+VALID_GRAPHML = (
+    '<graphml xmlns="http://graphml.graphdrawing.org/xmlns">'
+    '<graph edgedefault="directed">'
+    '<actionHistory><hash>hash-1</hash></actionHistory>'
+    '</graph>'
+    '</graphml>'
+)
+
+
+class FakeWorkFlowModel:
+    def __init__(self, graph_response):
+        self.graph_response = graph_response
+
+    def get(self, _server_id):
+        return self.graph_response
+
+
+class WorkflowControllerTests(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls):
+        server_root = pathlib.Path(__file__).resolve().parents[1]
+        if str(server_root) not in sys.path:
+            sys.path.insert(0, str(server_root))
+
+        fake_model_pkg = types.ModuleType('model')
+        fake_model_workflows = types.ModuleType('model.workflows')
+
+        class StubWorkFlowModel:
+            def get(self, _server_id):
+                return None
+
+        fake_model_workflows.WorkFlowModel = StubWorkFlowModel
+        fake_model_pkg.workflows = fake_model_workflows
+
+        sys.modules['model'] = fake_model_pkg
+        sys.modules['model.workflows'] = fake_model_workflows
+
+        if 'controller.workflow' in sys.modules:
+            del sys.modules['controller.workflow']
+        cls.workflow_module = importlib.import_module('controller.workflow')
+
+    def make_client(self, graph_response):
+        self.workflow_module.workFlowModel = FakeWorkFlowModel(graph_response)
+        app = Flask(__name__)
+        app.register_blueprint(self.workflow_module.workFlow, url_prefix='/workflow')
+        return app.test_client()
+
+    def test_missing_workflow_returns_404_for_none(self):
+        client = self.make_client(None)
+        response = client.get('/workflow/missing-id')
+        self.assertEqual(response.status_code, 404)
+        self.assertEqual(response.get_data(as_text=True), 'Not Found')
+
+    def test_missing_workflow_returns_404_for_legacy_tuple(self):
+        client = self.make_client((False, 'Record Not Found'))
+        response = client.get('/workflow/missing-id')
+        self.assertEqual(response.status_code, 404)
+        self.assertEqual(response.get_data(as_text=True), 'Not Found')
+
+    def test_hash_header_returns_400_for_different_history(self):
+        client = self.make_client(VALID_GRAPHML)
+        response = client.get('/workflow/existing-id', headers={'X-Latest-Hash': 'unknown-hash'})
+        self.assertEqual(response.status_code, 400)
+        self.assertEqual(response.get_data(as_text=True), 'Different History')
+
+    def test_hash_header_returns_200_for_matching_history(self):
+        client = self.make_client(VALID_GRAPHML)
+        response = client.get('/workflow/existing-id', headers={'X-Latest-Hash': 'hash-1'})
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.get_data(as_text=True), VALID_GRAPHML)
+
+
+if __name__ == '__main__':
+    unittest.main()