Check object if DbNull or Nothing and return Double value or 0

Question

I have a binding source which has datasource from datatable The table may have fields where its value is Null

When I code this, I get error : 'Public Function xTo0Double() As Double' has no parameters and its return type cannot be indexed

txt_inv_tot.Text = xTo0Double(bs_payh.Current("_INV_TOT")).ToString("N2")

Function xTo0Double(obj As Object) As Double
    If IsDbNullNothingEmpty(obj) Then
        Return 0
    Else
        Return CDbl(obj)
    End If
End Function

Function IsDbNullNothingEmpty(obj As Object) As Boolean            
        If obj Is Nothing
            Return True
        End If
        If IsDBNull(obj)
            Return True
        End If
        Try
            If String.IsNullOrEmpty(obj)
                Return True
            End If
        Catch ex As Exception

        End Try
        
        Return False
    End Function

I Did not understand why it gives error... I let the VS IDE correct the error, and it corrected like this

Function xTo0Double(obj As Object) As Object
    If IsDbNullNothingEmpty(obj) Then
        Return 0
    Else
        Return CDbl(obj)
    End If
End Function

But I want to return Double, not Object

All this coding to avoid using If Then End If in each time I want to check for field value before using it. for example this code works

If IsDBNull(bs_payh.Current("_INV_TOT"))
    txt_inv_tot.Text = "0.00"
Else
    txt_inv_tot.Text = CDbl(bs_payh.Current("_INV_TOT")).ToString("N2")
End If

But I don't want to use this way each time I want to read field value that could be Null

Is there is a way ?