I tried the same formula it is working for me...
can you please attached sample workbook it would be easy to help.
What is your expectation? You will see value only for 1 record where cola='wed' and other rows will get null only. Where you are seeing unexpected nulls?
I'm expecting a result of 12/1/18 as an output of the formula but instead am getting null.
U mean for all rows you are getting null?? if yes just check the data , it is case sensitive.