I already found another solution: I don't use a custom SortComparator.
Another solution would be to define a default value for null.
Would be nice if lucene in future would be able
to search by null values also if a custom SortComparator is used.
To tell you more:
public class MyComparator extends SortComparator {
...
public ScoreDocComparator newComparator (final IndexReader reader, final
String fieldname)
{
throws IOException {
final String field = fieldname.intern();
final Comparable[] cachedValues
= FieldCache.DEFAULT.getCustom (reader, field,
CollatorBasedComparator.this);
return new ScoreDocComparator() {
public int compare (ScoreDoc i, ScoreDoc j) {
... // compare and handle nulls
}
public Comparable sortValue (ScoreDoc i) {
return cachedValues[i.doc];
}
public int sortType(){
return org.apache.lucene.search.SortField.CUSTOM;
}
};
}
@Override
protected Comparable getComparable(String text) {
return new MyComparable(text); //implements compare(Object a,
Object b),
handles nulls
}
}
Using such a comparator will cause the exception above mentioned if null
values appear in the sort field.
That is because:
FieldDocSortedHitQueue 163-166:
case SortField.CUSTOM:{
c = docA.fields[i].compareTo(docB.fields[i]);
break;
}
does not check whether docA.fields[i] is null.
As you see in line 134-148:
case SortField.STRING:{
String s1 = (String) docA.fields[i];
String s2 = (String) docB.fields[i];
// null values need to be sorted first,
because of how
FieldCache.getStringIndex()
// works - in that routine, any
documents without a value in the given
field are
// put first. If both are null, the
next SortField is used
if (s1 == null) c = (s2==null) ? 0 : -1;
else if (s2 == null) c = 1; //
else if (fields[i].getLocale() == null)
{
c = s1.compareTo(s2);
} else {
c = collators[i].compare (s1,
s2);
}
break;
}
nulls are handled with the type SortField.STRING.
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