Avoid training CountVectorizer if no text is provided

[dakshvar22]

Proposed changes:

• Add a check for empty text list for a particular attribute before calling the fit function on CountVectorizer object.
• Train method only logs a warning now if some text is provided for an attribute, but still .fit() throws an exception.

Status (please check what you already did):

• made PR ready for code review
• reformat files using black (please check Readme for instructions)

[tmbo]

You branched of from master. please create a fresh branch from 1.3.x and cherry pick your commits to that branch. please open a new PR afterwards.

should be along the lines of

git checkout 1.3.x
git checkout -b bug-fix-count-vector-logging
git cherry-pick ebf556e

[dakshvar22]

@tmbo My bad. I think I did branch from 1.3.x but accidentally merged master into it. Will open a new PR.