Do not raise if error_code is missing from RestException (mlflow#1192)

mlflow/exceptions.py

@@ -37,7 +37,7 @@ def serialize_as_json(self):
 class RestException(MlflowException):
     """Exception thrown on non 200-level responses from the REST API"""
     def __init__(self, json):
-        error_code = json['error_code']
+        error_code = json.get('error_code', INTERNAL_ERROR)
         message = error_code
         if 'message' in json:
             message = "%s: %s" % (error_code, json['message'])

tests/utils/test_exception.py

@@ -1,6 +1,18 @@
-from mlflow.exceptions import ExecutionException
+from mlflow.exceptions import ExecutionException, RestException
 
 
 def test_execution_exception_string_repr():
     exc = ExecutionException("Uh oh")
     assert str(exc) == "Uh oh"
+
+
+def test_rest_exception_default_error_code():
+    exc = RestException({"message": "something important."})
+    assert "something important." in str(exc)
+
+
+def test_rest_exception_error_code_is_not_none():
+    error_string = "something important."
+    exc = RestException({"message": error_string})
+    assert "None" not in error_string
+    assert "None" not in str(exc)