API: Series.str wont' raise and now returns None (GH6106)
TST: add a test for columns with nested strings
Merge pull request #6108 from jreback/str

API: Series.str wont' raise and now returns None (GH6106)
ENH: ExcelWriter() accepts date and datetime formats

with ExcelWriter(date_format='YYYY-MM-DD', datetime_format='YYYY-MM-DD
HH:MM:SS') you can set the formatstrings for Excel export

BUG: xlsxwriter was not able to write date and datetime objects
Merge pull request #6107 from cpcloud/query-test-for-stringified-elements

TST: add a test for nested strings
TST: add tests for old version of numexpr