Failure to execute search request with empty top level filter

closes #3477

src/main/java/org/elasticsearch/index/query/IndexQueryParserService.java

@@ -20,6 +20,7 @@
 package org.elasticsearch.index.query;
 
 import com.google.common.collect.ImmutableMap;
+import org.apache.lucene.search.Filter;
 import org.apache.lucene.search.Query;
 import org.apache.lucene.util.CloseableThreadLocal;
 import org.elasticsearch.ElasticSearchException;
@@ -261,7 +262,11 @@ public class IndexQueryParserService extends AbstractIndexComponent {
     public ParsedFilter parseInnerFilter(XContentParser parser) throws IOException {
         QueryParseContext context = cache.get();
         context.reset(parser);
-        return new ParsedFilter(context.parseInnerFilter(), context.copyNamedFilters());
+        Filter filter = context.parseInnerFilter();
+        if (filter == null) {
+            return null;
+        }
+        return new ParsedFilter(filter, context.copyNamedFilters());
     }
 
     @Nullable

src/test/java/org/elasticsearch/test/integration/search/query/SimpleQueryTests.java

@@ -1231,6 +1231,13 @@ public class SimpleQueryTests extends AbstractSharedClusterTest {
         assertThat(response.getHits().totalHits(), equalTo(2l));
     }
 
+    @Test
+    public void testEmptyTopLevelFilter() {
+        client().prepareIndex("test", "type", "1").setSource("field", "value").setRefresh(true).execute().actionGet();
+        SearchResponse searchResponse = client().prepareSearch().setFilter("{}").execute().actionGet();
+        assertNoFailures(searchResponse);
+    }
+
     @Test // see #2926
     public void testMustNot() throws ElasticSearchException, IOException {
         client().admin().indices().prepareDelete().execute().actionGet();