LUCENE-3795: return empty array for TwoDoublesStrategy

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1301206 13f79535-47bb-0310-9956-ffa450edef68

modules/spatial/src/java/org/apache/lucene/spatial/vector/TwoDoublesStrategy.java

@@ -75,7 +75,7 @@ public class TwoDoublesStrategy extends SpatialStrategy<TwoDoublesFieldInfo> {
     if( !ignoreIncompatibleGeometry ) {
       throw new IllegalArgumentException( "TwoDoublesStrategy can not index: "+shape );
     }
-    return null;
+    return new IndexableField[0]; // nothing (solr does not support null)
   }
 
   @Override