diff --git a/gns3server/schemas/docker.py b/gns3server/schemas/docker.py
index 6acc159fd..e0aaa8867 100644
--- a/gns3server/schemas/docker.py
+++ b/gns3server/schemas/docker.py
@@ -41,7 +41,7 @@
         },
         "start_command": {
             "description": "Docker CMD entry",
-            "type": "string",
+            "type": ["string", "null"],
             "minLength": 0,
         },
         "image": {
@@ -78,7 +78,7 @@
         },
         "start_command": {
             "description": "Docker CMD entry",
-            "type": "string",
+            "type": ["string", "null"],
             "minLength": 0,
         }
     },
@@ -135,7 +135,7 @@
         },
         "start_command": {
             "description": "Docker CMD entry",
-            "type": "string",
+            "type": ["string", "null"],
             "minLength": 0,
         }
     },