[EP-tech] Patch: handle NULL values in EPrints::Search::Condition::Comparison

[leo at strike.wu.ac.at (Alexander 'Leo' Bergolth)]

Hi!

The attached patch changes SQL output to use "IS" instead of "=" when
comparing for equality against undefined values.

This fixes a problem (at least with Oracle databases) when using views
to browse by creators that have an empty givenname. (The SQL that was
created contained something like
"EPRINT_CREATORS_NAME"."CREATORS_NAME_GIVEN" = NULL
... which will never match.

I believe it could also correct several other problems concerning empty
fields, however, I did only stumble across the browse view issue yet.

Cheers,
--leo
-- 
e-mail   ::: Leo.Bergolth (at) wu.ac.at
fax      ::: +43-1-31336-906050
location ::: IT-Services | Vienna University of Economics | Austria

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