handle null query returning from query parsers properly

now that we support "null" queries, for example, when parsing a query and its lenient, make sure to handle it where applicable

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

@@ -166,6 +166,9 @@ public class FieldQueryParser implements QueryParser {
 
         try {
             query = queryParser.parse(qpSettings.queryString());
+            if (query == null) {
+                return null;
+            }
             query.setBoost(qpSettings.boost());
             query = optimizeQuery(fixNegativeQueryIfNeeded(query));
             if (query instanceof BooleanQuery) {

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

@@ -139,6 +139,9 @@ public class MatchQueryParser implements QueryParser {
         }
 
         Query query = matchQuery.parse(type, fieldName, text);
+        if (query == null) {
+            return null;
+        }
 
         if (query instanceof BooleanQuery) {
             Queries.applyMinimumShouldMatch((BooleanQuery) query, minimumShouldMatch);

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

@@ -169,6 +169,9 @@ public class MultiMatchQueryParser implements QueryParser {
         }
 
         Query query = multiMatchQuery.parse(type, fieldNames, text);
+        if (query == null) {
+            return null;
+        }
 
         if (query instanceof BooleanQuery) {
             Queries.applyMinimumShouldMatch((BooleanQuery) query, minimumShouldMatch);

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

@@ -210,6 +210,9 @@ public class QueryStringQueryParser implements QueryParser {
 
         try {
             query = queryParser.parse(qpSettings.queryString());
+            if (query == null) {
+                return null;
+            }
             query.setBoost(qpSettings.boost());
             query = optimizeQuery(fixNegativeQueryIfNeeded(query));
             if (query instanceof BooleanQuery) {