How to add IF null statement to current expression

[#1]

I am currently counting First discovered dates, how would i add

"count first discovered within the last month IF Closed_mitigated_On is null'

Open:

Count({$<First_Discovered={'>=$(=MonthStart(Today()))<=$(=Today())'}> } First_Discovered)

Also, I am looking to add a compliance flag into this this chart. How would I write Count(compliance_flag for the last month)

the above count statement isn't working.

[#2]

No difference

[vinieme12]

what is the format of this field: First_Discovered

[#4]

MM/DD/YYYY

[vinieme12]

Try, for previous Month data

=Count({$<First_Discovered={">=$(=DATE(Addmonths(Today(),-1),'MM/DD/YYYY'))<$(=DATE(MonthStart(Today()),'MM/DD/YYYY'))"}> } First_Discovered)