Created attachment 199168 [details]
Macro Main shows the problem

If a function declares a Variant parameter, and if this parameter may be used as an object somewhere in the function, it is no longer possible to call this function with a non objet parameter.

For exemple :
Function example(param as Variant)
	If IsObject(param) Then : result = param.getURL()
	Else                    : result = "param is not an object"
	End If
	example() = result
End Function

Calling example(ThisComponent) is OK and returns the document URL
But calling example("a string") generate an error "undefined parameter"

The error doesn't appear if param is not used as an objet. For instance by copying it to a local variable, replacing  
result = param.getURL()
by 
obj = param: result = obj.getURL()