diff --git a/clearml/backend_interface/task/args.py b/clearml/backend_interface/task/args.py
index b850b403..b54312e3 100644
--- a/clearml/backend_interface/task/args.py
+++ b/clearml/backend_interface/task/args.py
@@ -528,8 +528,10 @@ class _Arguments(object):
                     "Failed parsing task parameter {}={} keeping default {}={}".format(k, param, k, v)
                 )
 
-            # assume more general purpose type int -> float
-            if v_type == int:
+            # if parameter is empty and default value is None, keep as None
+            if param == '' and v is None:
+                v_type = type(None)
+            elif v_type == int:  # assume more general purpose type int -> float
                 if v is not None and int(v) != float(v):
                     v_type = float
             elif v_type == bool:
diff --git a/clearml/model.py b/clearml/model.py
index 146f1404..b7ccc4bd 100644
--- a/clearml/model.py
+++ b/clearml/model.py
@@ -2347,6 +2347,7 @@ class OutputModel(BaseModel):
         iteration=None,  # type: Optional[int]
         update_comment=True,  # type: bool
         is_package=False,  # type: bool
+        async_enable=True,  # type: bool
     ):
         # type: (...) -> str
         """
@@ -2374,6 +2375,8 @@ class OutputModel(BaseModel):
             - ``True`` - Update model comment (Default)
             - ``False`` - Do not update
         :param bool is_package: Mark the weights file as compressed package, usually a zip file.
+        :param bool async_enable: Whether to upload model in background or to block.
+            Will raise an error in the main thread if the weights failed to be uploaded or not.
 
         :return: The uploaded URI.
         """
@@ -2421,6 +2424,7 @@ class OutputModel(BaseModel):
                     target_filename=target_filename or Path(weights_filename).name,
                     auto_delete_file=auto_delete_file,
                     iteration=iteration,
+                    async_enable=async_enable
                 )
 
             # make sure we delete the previous file, if it exists
@@ -2502,7 +2506,7 @@ class OutputModel(BaseModel):
             output_uri = model.update_and_upload(
                 model_file=weights_filename,
                 task_id=self._task.id,
-                async_enable=True,
+                async_enable=async_enable,
                 target_filename=target_filename,
                 framework=self.framework or framework,
                 comment=comment,
@@ -2535,6 +2539,7 @@ class OutputModel(BaseModel):
         target_filename=None,  # type: Optional[str]
         auto_delete_file=True,  # type: bool
         iteration=None,  # type: Optional[int]
+        async_enable=True,  # type: bool
     ):
         # type: (...) -> str
         """
@@ -2559,6 +2564,8 @@ class OutputModel(BaseModel):
             - ``False`` - Do not delete
 
         :param int iteration: The iteration number.
+        :param bool async_enable: Whether to upload model in background or to block.
+            Will raise an error in the main thread if the weights failed to be uploaded or not.
 
         :return: The uploaded URI for the weights package.
         """
@@ -2626,6 +2633,7 @@ class OutputModel(BaseModel):
             target_filename=target_filename or "model_package.zip",
             iteration=iteration,
             update_comment=False,
+            async_enable=async_enable
         )
         # set the model tag (by now we should have a model object) so we know we have packaged file
         self._set_package_tag()