Add empty initialisation for models

Created by: stefanoborini

Allows for models to be initialised without JSON data, but just from the default content (traits instantiation)

force_bdss/core_plugins/csv_extractor/csv_extractor/csv_extractor_bundle.py

@@ -11,8 +11,11 @@ from .csv_extractor_data_source import CSVExtractorDataSource
 class CSVExtractorBundle(HasStrictTraits):
     name = String("csv_extractor")
 
-    def create_model(self, model_data):
-        return CSVExtractorModel.from_json(model_data)
+    def create_model(self, model_data=None):
+        if model_data is None:
+            return CSVExtractorModel()
+        else:
+            return CSVExtractorModel.from_json(model_data)
 
     def create_data_source(self, application, model):
         return CSVExtractorDataSource(self, application, model)