Issue - 27482 : fixed isnull attribute for type objects

[AlejandroGuariguata]

• [yes] closes pd.isnull() raises AttributeError on Pandas type objects #27482
• [yes] tests added / passed
• passes black pandas
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• [yes] whatsnew entry

[pep8speaks]

Hello @AlejandroGuariguata! Thanks for opening this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file pandas/core/dtypes/missing.py:

Line 130:55: W291 trailing whitespace
Line 131:22: E711 comparison to None should be 'if cond is None:'
Line 131:30: W291 trailing whitespace
Line 133:5: E722 do not use bare 'except'

• In the file scripts/tests/test_27482.py:

Line 5:1: E302 expected 2 blank lines, found 1
Line 6:1: W191 indentation contains tabs
Line 6:1: W293 blank line contains whitespace
Line 7:1: W191 indentation contains tabs
Line 7:2: E117 over-indented
Line 8:1: W191 indentation contains tabs
Line 8:3: E117 over-indented
Line 8:19: E231 missing whitespace after ','
Line 8:21: E231 missing whitespace after ','
Line 8:23: E231 missing whitespace after ','
Line 9:1: W191 indentation contains tabs
Line 10:1: W191 indentation contains tabs
Line 10:23: E225 missing whitespace around operator
Line 10:23: E712 comparison to False should be 'if cond is False:' or 'if not cond:'
Line 10:30: E231 missing whitespace after ','
Line 12:1: W191 indentation contains tabs
Line 13:1: W191 indentation contains tabs
Line 13:3: E117 over-indented
Line 13:30: E231 missing whitespace after ','
Line 13:32: E231 missing whitespace after ','
Line 13:34: E231 missing whitespace after ','
Line 14:1: W191 indentation contains tabs
Line 15:1: W191 indentation contains tabs
Line 15:23: E225 missing whitespace around operator
Line 15:23: E712 comparison to False should be 'if cond is False:' or 'if not cond:'
Line 15:30: E231 missing whitespace after ','
Line 19:20: W292 no newline at end of file

[TomAugspurger]

Thanks @AlejandroGuariguata, but we had #27664 working on this.