message: XPath: alloc_string no longer returns NULL
  NULL return value will be reserved for the OOM error indicator.
diff: @@ -10953,8 +10953,9 @@ PUGI__NS_BEGIN
  const char_t* alloc_string(const xpath_lexer_string& value)
  {
  - if (value.begin)
  - {
  + if (!value.begin)
  + return PUGIXML_TEXT("");
  +
  size_t length = static_cast<size_t>(value.end - value.begin);
  char_t* c = static_cast<char_t*>(_alloc->allocate_nothrow((length + 1) * sizeof(char_t)));
  @@ -10966,8 +10967,6 @@ PUGI__NS_BEGIN
  return c;
  }
  - else return 0;
  - }
  xpath_ast_node* parse_function_helper(ast_type_t type0, ast_type_t type1, size_t argc, xpath_ast_node* args[2])
  {
  