Replaced exact lookups of the empty string with isnull lookups in Oracle.  Fixes the testPreventDuplicateComments case.
Replaced exact lookups of the empty string with isnull lookups in Oracle.  Fixes the testPreventDuplicateComments case.

git-svn-id: 554f83ef17aa7291f84efa897c1acfc5d0035373@8827 bcc190cf-cafb-0310-a4f2-bffc1f526a37

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