TYPE luaQ_optqvariant<TYPE>(lua_State *L, int index, TYPE d = TYPE())
Returns the optional Qt variant of actual type TYPE
found at position index
in the stack. If the position
corresponds to an unspecified function argument,
this function returns d
. If the Lua value at this position
cannot be converted to the requested type, this function
causes an error.
See also luaQ_checkqvariant