SOLR-15031 Prevent null being wrapped in a QueryValueSource

closes #2118

lucene/queries/src/java/org/apache/lucene/queries/function/valuesource/QueryValueSource.java

@@ -42,6 +42,10 @@ public class QueryValueSource extends ValueSource {
   final float defVal;
 
   public QueryValueSource(Query q, float defVal) {
+    super();
+    if (q == null) {
+      throw new IllegalArgumentException("query cannot be null");
+    }
     this.q = q;
     this.defVal = defVal;
   }

solr/CHANGES.txt

@@ -268,6 +268,9 @@ Bug Fixes
 
 * SOLR-14939: JSON range faceting to support cache=false parameter. (Christine Poerschke, Mike Drob)
 
+* SOLR-15031: Fix preventing null being wrapped in a QueryValueSource subQuery. Such null queries can be caused by query text
+  resulting in an empty token stream. (Pieter van Boxtel via Mike Drob)
+
 Other Changes
 ---------------------
 

solr/core/src/java/org/apache/solr/search/FunctionQParser.java

@@ -361,7 +361,9 @@ public class FunctionQParser extends QParser {
         ((FunctionQParser)subParser).setParseMultipleSources(true);
       }
       Query subQuery = subParser.getQuery();
-      if (subQuery instanceof FunctionQuery) {
+      if (subQuery == null) {
+        valueSource = new ConstValueSource(0.0f);
+      } else if (subQuery instanceof FunctionQuery) {
         valueSource = ((FunctionQuery) subQuery).getValueSource();
       } else {
         valueSource = new QueryValueSource(subQuery, 0.0f);

solr/core/src/test/org/apache/solr/search/function/TestFunctionQuery.java

@@ -1148,4 +1148,17 @@ public class TestFunctionQuery extends SolrTestCaseJ4 {
         /*id*/1, /*score*/2,
         /*id*/2, /*score*/2);
   }
+
+  /**
+   * Tests a specific (edge) case where a subQuery is null, because no terms are
+   * found in the query. Below such subQuery is created from a field query on a
+   * query text containing only stopwords. Feeding the resulting null-subQuery
+   * into a QueryValueSource (and then using it in for example an if function)
+   * may not produce NullPointerExceptions.
+   */
+  @Test
+  public void testNullSubQuery() throws Exception {
+    clearIndex();
+    assertJQ(req("q", "{!func}if($subQuery,1,0)", "subQuery", "{!field f=text v='stopworda'}"));
+  }
 }