CRM-15522 make "Null" not evaluate as null if N is capitalized

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* CRM-15522: Last name Null disappears
  https://issues.civicrm.org/jira/browse/CRM-15522
Merge pull request #79 from agh1/null-name

CRM-15522 make "Null" not evaluate as null if N is capitalized
Looks like we have consensus that this is safe to merge.