I'm not sure but I'm not able to replicate the issue here...
this is with both an actual blank as well as NULL value...
You can read up on the function here...
https://support.office.com/en-us/article/FREQUENCY-function-44e3be2b-eca0-42cd-a3f7-fd9ea898fdb9
Unknown[TABLE="class: grid, width: 300"]
<tbody>[TR="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=DAE7F5]#DAE7F5[/URL] "]
[TD][/TD]
[TD]F[/TD]
[TD]G[/TD]
[TD]H[/TD]
[TD]I[/TD]
[/TR]
[TR]
[TD="align: center"]1[/TD]
[TD="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=FAFAFA]#FAFAFA[/URL] "]JC[/TD]
[TD="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=FAFAFA]#FAFAFA[/URL] , align: right"]10/22/2017[/TD]
[TD="align: right"][/TD]
[TD="align: right"][/TD]
[/TR]
[TR]
[TD="align: center"]2[/TD]
[TD="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=FAFAFA]#FAFAFA[/URL] "]JC[/TD]
[TD="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=FAFAFA]#FAFAFA[/URL] , align: right"]10/22/2017[/TD]
[TD="align: right"][/TD]
[TD="align: right"][/TD]
[/TR]
[TR]
[TD="align: center"]3[/TD]
[TD="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=FAFAFA]#FAFAFA[/URL] "]AF[/TD]
[TD="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=FAFAFA]#FAFAFA[/URL] , align: right"]10/22/2017[/TD]
[TD="align: right"][/TD]
[TD="align: right"]3[/TD]
[/TR]
[TR]
[TD="align: center"]4[/TD]
[TD="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=FAFAFA]#FAFAFA[/URL] "]BE[/TD]
[TD="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=FAFAFA]#FAFAFA[/URL] , align: right"]10/17/2017[/TD]
[TD="align: right"][/TD]
[TD="align: right"][/TD]
[/TR]
[TR]
[TD="align: center"]5[/TD]
[TD="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=FAFAFA]#FAFAFA[/URL] "]JC[/TD]
[TD="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=FAFAFA]#FAFAFA[/URL] , align: right"]10/15/2015[/TD]
[TD="align: right"][/TD]
[TD="align: right"][/TD]
[/TR]
[TR]
[TD="align: center"]6[/TD]
[TD="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=FAFAFA]#FAFAFA[/URL] "]JC[/TD]
[TD="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=FAFAFA]#FAFAFA[/URL] , align: right"]10/14/2017[/TD]
[TD="align: right"][/TD]
[TD="align: right"][/TD]
[/TR]
[TR]
[TD="align: center"]7[/TD]
[TD="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=FAFAFA]#FAFAFA[/URL] "]JC[/TD]
[TD="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=FAFAFA]#FAFAFA[/URL] , align: right"]10/14/2017[/TD]
[TD="align: right"][/TD]
[TD="align: right"][/TD]
[/TR]
[TR]
[TD="align: center"]8[/TD]
[TD="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=FAFAFA]#FAFAFA[/URL] "]JC[/TD]
[TD="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=FAFAFA]#FAFAFA[/URL] "][/TD]
[TD="align: right"][/TD]
[TD="align: right"][/TD]
[/TR]
[TR]
[TD="align: center"]9[/TD]
[TD="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=FAFAFA]#FAFAFA[/URL] "]AF[/TD]
[TD="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=FAFAFA]#FAFAFA[/URL] , align: right"]10/22/2017[/TD]
[TD="align: right"][/TD]
[TD="align: right"][/TD]
[/TR]
[TR]
[TD="align: center"]10[/TD]
[TD="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=FAFAFA]#FAFAFA[/URL] "]JC[/TD]
[TD="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=FAFAFA]#FAFAFA[/URL] , align: right"][/TD]
[TD="align: right"][/TD]
[TD="align: right"][/TD]
[/TR]
</tbody>[/TABLE]
Data
[TABLE="width: 85%"]
<tbody>[TR]
[TD]
Worksheet Formulas[TABLE="width: 100%"]
<tbody>[TR="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=DAE7F5]#DAE7F5[/URL] "]
[TH]Cell[/TH]
[TH="align: left"]Formula[/TH]
[/TR]
[TR]
[TH="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=DAE7F5]#DAE7F5[/URL] "]G8[/TH]
[TD="align: left"]=""[/TD]
[/TR]
</tbody>[/TABLE]
[/TD]
[/TR]
</tbody>[/TABLE]
[TABLE="width: 85%"]
<tbody>[TR]
[TD]
Array Formulas[TABLE="width: 100%"]
<tbody>[TR="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=DAE7F5]#DAE7F5[/URL] "]
[TH]Cell[/TH]
[TH="align: left"]Formula[/TH]
[/TR]
[TR]
[TH="bgcolor: [URL=https://www.mrexcel.com/forum/usertag.php?do=list&action=hash&hash=DAE7F5]#DAE7F5[/URL] "]I3[/TH]
[TD="align: left"]{=SUM(
IF(FREQUENCY(IF(Data!F1:F10="JC",Data!G1:G10),Data!G1:G10),1))}[/TD]
[/TR]
</tbody>[/TABLE]
Entered with Ctrl+Shift+Enter. If entered correctly, Excel will surround with curly braces {}.
Note: Do not try and enter the {} manually yourself[/TD]
[/TR]
</tbody>[/TABLE]