DISI.iterator() should never return null. [LUCENE-5117]

[asfimport]

If you have a Filter, you have to check for null twice: Filter.getDocIDSet() can return a null DocIDSet, and then DocIDSet.iterator() can return a null iterator.

There is no reason for this: I think iterator() should never return null (consistent with terms/postings apis).

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Migrated from LUCENE-5117 by Robert Muir (@rmuir), updated Oct 23 2014

[asfimport]

Michael McCandless (@mikemccand) (migrated from JIRA)

+1

[asfimport]

Adrien Grand (@jpountz) (migrated from JIRA)

+1

[asfimport]

Uwe Schindler (@uschindler) (migrated from JIRA)

Damn, fix this. It's horrible with those null checks! :-)

[asfimport]

Robert Muir (@rmuir) (migrated from JIRA)

I am working on it. I am reviewing all uses of this method...

[asfimport]

Robert Muir (@rmuir) (migrated from JIRA)

After investigation there are a few concerns of mine:

• today, there are some uses of DISI not checking the result of iterator()
• changing the API here is kinda a "break" (maybe should be 5.0 only?)
• I am not totally happy with the change because of Weight.scorer can return a null Scorer (which is a DISI). Although this is "unrelated" to DISI.iterator(), its still a potential cause for bugs.

Maybe there is a better solution I'm not thinking of too...

[asfimport]

Adrien Grand (@jpountz) (migrated from JIRA)

Would it be possible to fix Weight.scorer to never return null too?

[asfimport]

Robert Muir (@rmuir) (migrated from JIRA)

not today. because then there would be no way for it to represent this case.

DISI is different, because it the docidset itself could be null so it loses nothing if we try to simplify this.