Coalesce and IsNULL in a Concat not working with NULL valies

Question

I am trying to create a string out of several fields, some of which can be NULL. If I do

Select Concat(FieldA,IsNULL(FieldB,''),FIeldC) from Table

I get

1582 - Incorrect parameter count in the call to native function 'IsNULL'

If I do

Select Concat(FieldA,Coalesce(FieldB,''),FIeldC) from Table

I get NULL records where FieldB is NULL I even tried for the heck of it:

 Select Concat(FieldA,IFNULL(FieldB,''),FIeldC) from Table

and got empty records again

Perhaps I'm misunderstanding but I thought the whole point was to return either the record value or an empty value on NULL records to avoid null returns