Regression: Invalid assertion in string assign (and probably other functions)

[liss-h]

boost::container::string::assign checks BOOST_ASSERT(s != 0)

container/include/boost/container/string.hpp

Lines 1662 to 1666 in a42e8ba

	basic_string& assign(const CharT* s, size_type n)
	{
	BOOST_ASSERT(s != 0);
	return this->assign(s, s + difference_type(n));
	}

This is invalid for default constructed std::string_view.

"1) Default constructor. Constructs an empty std::basic_string_view. After construction, data() is equal to nullptr, and size() is equal to 0." - https://en.cppreference.com/cpp/string/basic_string_view/basic_string_view

The check should have been BOOST_ASSERT(s != nullptr || n == 0);