Can you spot the problem (VBx/VB.NET)

imports Microsoft.VisualBasic
imports System

public module MyModule
    sub Main
        dim a as integer = 0
        dim b as integer = CInt(iif(a=0, 100, SomeCalc(a)))
    end sub
    
    private function SomeCalc(a as integer) as integer
        if a = 0 then
            throw new ArgumentNullException("a")
        else
            return CInt(100 / a)
        end if
    end function
end module