fixed bug (#566)

Author: mingkang111

ads/aqua/extension/model_handler.py

@@ -32,7 +32,7 @@ def read(self, model_id):
  @exception_handler
  def list(self):
  """List Aqua models."""
- compartment_id = self.get_argument("compartment_id")
+ compartment_id = self.get_argument("compartment_id", default=None)
  # project_id is no needed.
  project_id = self.get_argument("project_id", default=None)
  return self.finish(AquaModelApp().list(compartment_id, project_id))