%%[ var @this set @this = FieldName]%% %%[IF @this == "" or @this is NULL THEN]%% some text here to signify that it's blank %%[ELSE]%% %%FieldName%%, %%[ENDIF]%%
%%[ var @this set @this = FieldName]%%
%%[IF @this == "" or @this is NULL THEN]%%
some text here to signify that it's blank
%%[ELSE]%% %%FieldName%%,
%%[ENDIF]%%
Taken from: https://help.salesforce.com/articleView?id=000213691&type=1