hotspot/src/share/vm/services/diagnosticArgument.cpp:
template <> void DCmdArgument<MemorySizeArgument>::parse_value(const char* str,
                                                  size_t len, TRAPS) {
  if (str == NULL) {
    THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(),
              "Integer parsing error nanotime value: syntax error");
  }

There are typo in message for str == NULL. It was copy/pasted from nanotime error message. It should be changed to the "Parsing error memory size value: syntax error, value is null" to be consistent with other error messages for memory size arguments.