Index: lucene/contrib/queries/src/java/org/apache/lucene/search/BooleanFilter.java
===================================================================
--- lucene/contrib/queries/src/java/org/apache/lucene/search/BooleanFilter.java	(revision 1207773)
+++ lucene/contrib/queries/src/java/org/apache/lucene/search/BooleanFilter.java	(working copy)
@@ -47,8 +47,10 @@
   public DocIdSet getDocIdSet(IndexReader reader) throws IOException {
     FixedBitSet res = null;
     
+    boolean hasShouldClauses = false;
     for (final FilterClause fc : clauses) {
       if (fc.getOccur() == Occur.SHOULD) {
+        hasShouldClauses = true;
         final DocIdSetIterator disi = getDISI(fc.getFilter(), reader);
         if (disi == null) continue;
         if (res == null) {
@@ -57,6 +59,8 @@
         res.or(disi);
       }
     }
+    if (hasShouldClauses && res == null)
+      return DocIdSet.EMPTY_DOCIDSET;
     
     for (final FilterClause fc : clauses) {
       if (fc.getOccur() == Occur.MUST_NOT) {