validate should treat null values as empty strings

[cmawhorter]

This is wrong:

urn-lib/src/lib/validate.js

Lines 19 to 20 in 7b33d42

	if (null === str) str = '';
	else if (!isString(str)) return false;

It should be:

  if (null === str) { str = ''; }
  // and then
  if (!isString(str)) return false;