BloombergLP::bslstl::Function_InvokerUtilNullCheck

Provides an isNull static method that that returns whether or not its argument is "null", i.e., it cannot be invoked. For must FUNC types isNull always returns false as every instance of FUNC is invocable. However, specializations of this class, especially for pointer types, have isNull functions that sometimes return true. This class is a customization point: types outside of this component can (but rarely should) specialize this template. In particular, bslstl_function contains a specialization for bsl::function.