Correct ValueError invalid type promotion exception
- [x] closes #12599
- [x] tests added / passed
- [x] passes `git diff upstream/master | flake8 --diff`
- [x] whatsnew entry

Please review
 add a whatsnew. you should always add a whatsnew and tests on the very first push. that way I can look at an already done PR and just comment on changes, rather than having to go back and forth so much.
 @jreback The reason I'm not adding a whatnews early, as it conflicts (very) frequently ... I will rebase/squash in a minute.
Maybe whatsnew could be generated from the commit logs (instead of constantly rebasing on the same section of a single file)?
 I thought I explained this

first it doesn't really matter if he whatsnew conflicts - usually these go thru several iterations

next you simply put them NOT AT THE END then you won't have conflicts - this is the reason for the blank lines in the bug fixes section
 Added whatsnew
 thanks @gliptak 
