( Blank ) categories are appearing for no reason

[halkosj]

When generating categories, Transformer sometimes creates a category called "( Blank )".  What is that for? What causes it? How do we get rid of it permanently?

We can manually delete the category, but we have to remember to do that every time we generate categories or create a new cube.

The underlying data in the database has no blanks or nulls - so why does transfomer think a ( Blank ) category is required?