Keep null values in text data types for dataflows

When pulling null values from a text data types in a dataflow it currently pull blank text string rather than a null. This is meaning a transform is then required in the dataset to transform it back to a null. This creates a few issues, 1) if the data requires a differentiation between a null and a blank it is impossible to get this value back (unless a secondary column to indicate the nulls) 2) means that an analyst needs to remember to transform the column in the every dataset it is used 3) if a dax formula is used to count the nulls for a calculation this won't report correctly unless the analyst remembers to do the transform.