Problems with passing decimals to vba - ms-access

Question

I am having some trouble passing a decimal number from an access field (using a DAO recordset) to a vba variable. I have tried changing datatypes in access and vba (single / currency), but the same line keeps being highlighted in the debugger, with a Runtime error 94 "Invalid use of null".
The thing that is confusing me is, when I hold the cursor over the variable in the debugger; the quickinfo shows that the variable is holding the correct value, but the recordset field is null. This only happens for the Decimal field, Other fields (string / integer) are not highlighted.
The line that is higlighted in the debugger is rs!Field4 in the 'Start Loop block. The strange thing is that rs.Field3 sets the numField3 variable fine. The only difference between the two is that field 3 contains integers and field 4 contains decimals. Both were msAccess numbers, but i have changed to currency during problem solve.
Any feedback would be good
Thanks
Private Sub Command1_Click()
'Set Database and Recordset variables
Dim thisDB As DAO.Database
Dim rs As DAO.Recordset
Set thisDB = CurrentDb
Set rs = thisDB.OpenRecordset("tblTable1")
'Declare and set recordset variables variables
Dim strField1 As String
Dim strField2 As String
Dim numField3 As Currency
Dim numField4 As Currency
Dim dtField5 As Date
Dim dtField6 As Date
'Declare dynamic variables
Dim dtVar1 As Date
Dim intVar2 As Integer
Dim dtVar3 As Date
'DecalreSQL Variables
Dim num1 As Currency
Dim num2 As Currency
Dim num3 As Currency
Dim StrSQL As String
Dim strValues As String
'Start Loop
Do While Not rs.EOF
strField1 = rs!Field1
strField2 = rs!Field2
numField3 = rs!Field3
numField4 = rs!Field4
dtField5 = rs!Field5
dtField6 = rs!Field6
If strField1 = "This" And strField2 = "That" Then
'Perform calculations
dtVar1 = 0
dtVar3 = 0
num3 = 0
Do While dtVar3 < dtField6
If ’Something’ Then
This calculation sets variables
ElseIf ‘SomethingElse’ Then
This calculation sets variables
Else
This calculation sets variables
End If
'Build SQL Query and apprend to table
strValues = dtVar1& "," & num1 & "," &num2 & "," & num3
StrSQL = "INSERT INTO tblTable2 (Field1, Field2, Field3, Field4 );"
StrSQL = StrSQL & "VALUES ('" & strValues & "')"
DoCmd.SetWarnings False
DoCmd.RunSQL StrSQL
DoCmd.SetWarnings True
dtVar3 = dtVar1
Loop
End If
rs.MoveNext
Loop
rs.Close
End Sub

Answer 1

When you hold the cursor over the variable it hasn't been assigned yet. You're actually showing the last record's value that was assigned to the numField4 variable.
What that means is your current recordset field Field4 is actually a null. To assign it to the numeric variable you need to trap for that condition.
numField4 = Nz(rs!Field4, 0)
And you should probably repeat for Field3 to cover thst possibility too