Duplicate Field Name Message

[shawnbrown]

DataSource raises a confusing error message when it fails to load data because of duplicate field names.

When data has multiple columns named "x":

ValueError: Duplicate values: x

When data has multiple columns where the name is blank:

ValueError: Duplicate values: 

The error message should indicate that the "values" are actually field names. And in the case of blank field names, the error message should address this more clearly rather than trying to show a blank value.

[shawnbrown]

This is done: 2e200e2bb7d9a8016bcb6e908d4a8b12db8e2568

Now, when data has multiple columns named "x":

ValueError: data contains multiple fields named 'x' (field names must be unique)

Now, when data has multiple columns where the name is blank:

ValueError: data contains multiple fields where the name is blank (field names must be unique)