This should be simple, but what is the syntax I can use to catch a blank field? I have tried variations of the StudentID = 0 and or trying to catch sTDJC being null, but it doesn't like the syntax or falls through to sTDCJ.

What I am trying to do is catch an empty TDCJ field so that unless it is not blank it never gets to the sTDCJ entry and forces the user to put a value in the TDCJ field.

Right now when TDCJ is blank I get an error, Invalid use of Null.


    StudentID = Nz(DLookup("StudentID", "StudentT", "TDCJ=""" & TDCJ & """"), 0)
  
    If StudentID > 0 Then
      ' TDJC Number found, Lookup Info
            TDCJ = DLookup("TDCJ", "StudentT", "StudentID=" & StudentID)
            MsgBox ("Student exist, verify TDCJ #, and Re-Enter")
            TDCJ = Null
            LastName = Null
            FirstName = Null
            DOB = Null
            Unit = Null
            Address = Null
            City = Null
            State = Null
            ZIP = Null
            TDCJ.SetFocus
      
   Else: StudentID = 0
      ' TDJC Number NOT found, add New Student Info
            sTDCJ = TDCJ
            sLastName = LastName
            sFirstName = FirstName
            sDOB = DOB
            sUnit = Unit
            sAddress = Address
            sCity = City
            sState = State
            sState = UCase(sState)
            sZIP = ZIP
          
            SQL = "INSERT INTO StudentT ( TDCJ, LastName, FirstName, DOB, UNIT, Address, City, State, ZIP ) " & _
                    "SELECT """ & sTDCJ & """, """ & sLastName & """, """ & sFirstName & """, """ & sDOB & """, """ & sUnit & """, """ & _
                    sAddress & """, """ & sCity & """, """ & sState & """, """ & sZIP & """"
            
            DoCmd.RunSQL SQL
          
        End If
        
    End Sub