TopGroupsCollector#getTopGroups() returns NaN maxScore when no hits for a group value

[gaobinlong]

Description

In TopGroupsCollector#getTopGroups() method, if there're no hits for a group value, then groupMaxScore is NaN:

lucene/lucene/grouping/src/java/org/apache/lucene/search/grouping/TopGroupsCollector.java

Line 178 in 1f0bc36

allTopDocs.scoreDocs.length == 0 ? Float.NaN : allTopDocs.scoreDocs[0].score;

, this causes the following code Math.max(maxScore, groupMaxScore) always returns NaN in the next for loop, so the final maxScore is NaN.

lucene/lucene/grouping/src/java/org/apache/lucene/search/grouping/TopGroupsCollector.java

Line 207 in 1f0bc36

maxScore = Math.max(maxScore, groupMaxScore);

.

See the debug info:

We should use the same way like TopGroups#nonNANmax() to avoid that issue:

lucene/lucene/grouping/src/java/org/apache/lucene/search/grouping/TopGroups.java

Line 98 in 1f0bc36

private static float nonNANmax(float a, float b) {

Need to check if other places have the same issue.

Version and environment details

All versions.