The C standard says in 6.3.2.3, paragraph 4:

Conversion of a null pointer to another pointer type yields a null pointer of that type. Any two null pointers shall compare equal.

C++ appears to be incompatible with the first sentence in only two areas:

    A *a = 0;
    void *v = a;

C++ (7.3.12 [conv.ptr] paragraph 2) says nothing about the value of v.

    void *v = 0;
    A *b = (A*)v; // aka static_cast<A*>(v)

C++ (7.6.1.9 [expr.static.cast] paragraph 10) says nothing about the value of b.

Suggested changes:

1. Add the following sentence to 7.3.12 [conv.ptr] paragraph 2:

The null pointer value is converted to the null pointer value of the destination type.

2. Add the following sentence to 7.6.1.9 [expr.static.cast] paragraph 10:

The null pointer value (7.3.12 [conv.ptr]) is converted to the null pointer value of the destination type.