[BUG] Extend fill_empty's column_names type range

[Zeroto521]

PR Description

Please describe the changes proposed in the pull request:

• Let column_names support more type range, from list & tuple to Iterable.

This PR resolves #998.

PR Checklist

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1. PR in from a fork off your branch. Do not PR from <your_username>:dev, but rather from <your_username>:<feature-branch_name>.

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Relevant Reviewers

Please tag maintainers to review.

• @ericmjl

[codecov]

Codecov Report

Merging #1014 (a4a8b4f) into dev (d3146bb) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##              dev    #1014   +/-   ##
=======================================
  Coverage   96.54%   96.54%           
=======================================
  Files          77       77           
  Lines        2835     2836    +1     
=======================================
+ Hits         2737     2738    +1     
  Misses         98       98           

[ericmjl]

@Zeroto521 I'd love to merge, but before we do so, would love to hear your thoughts on the above discussion point!

[ericmjl]

Thank you, @Zeroto521 for this contribution!