ERROR showing up instead of 0 in SSRS report

new to report builder, I'm trying to solve an issue where the grand total in the report is showing #error instead of 0. Error in Grand Total

Here's the expression for the field:

=Code.Divide(Microsoft.VisualBasic.Strings.FormatNumber(Sum(Fields!InExtCost.Value, "ClassDesc"), 5), Microsoft.VisualBasic.Strings.FormatNumber(Sum(Fields!InTranQty.Value, "ClassDesc"),  First(Fields!DecimalsQuantity.Value, "RptParameter")))

Divide is the custom code written:

Public Function Divide(ByVal dividend As Double, ByVal divisor As Double) As Double
   If IsNothing(divisor) Or divisor = 0 Or IsNothing(dividend) Or dividend = 0 Then
      Return 0
   Else
      Return dividend / divisor
   End If
End Function

I've tried using the code to run 0 divide by 1 and 1 divide 0 and both of them shows up 0 in the report preview, I'm expecting it to show up 0 if either dividend or divisor is 0.

Maybe there are NULL values causing the error.

In any case i created a sample dataset with a mix of values

SELECT 50.123456789 AS InExtCost, 10.123456789 As InTranQty   UNION ALL
SELECT 50.123456789 AS InExtCost, 0 As InTranQty   UNION ALL
SELECT  0 AS InExtCost, 10.123456789 As InTranQty   UNION ALL
SELECT  0 AS InExtCost,  0 As InTranQty       UNION ALL
SELECT NULL AS InExtCost, 0 As InTranQty    UNION ALL
SELECT 0 AS InExtCost, NULL As InTranQty    UNION ALL
SELECT 1 AS InExtCost, NULL As InTranQty    UNION ALL
SELECT NULL AS InExtCost, 1 As InTranQty 

In your expression I have added a conversion to double using Cdbl function

=Code.Divide(   Microsoft.VisualBasic.Strings.FormatNumber(Sum(Cdbl(Fields!InExtCost.Value), "ClassDesc"), 5)
, Microsoft.VisualBasic.Strings.FormatNumber(Sum(Cdbl(Fields!InTranQty.Value), "ClassDesc"),  First(Fields!DecimalsQuantity.Value, "RptParameter"))
)

Now that each parameter your are passing to the Divide function is double you can simplify it (or leave it as it is)

Public Function Divide(ByVal dividend As Double, ByVal divisor As Double) As Double
   If     divisor = 0 Then
      Return 0
   Else
      Return dividend / divisor
   End If
End Function