check null or exists before deleting file

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1593884 13f79535-47bb-0310-9956-ffa450edef68

solr/test-framework/src/java/org/apache/solr/SolrTestCaseJ4.java

@@ -1013,6 +1013,7 @@ public abstract class SolrTestCaseJ4 extends LuceneTestCase {
   }
 
   public static boolean recurseDelete(File f) {
+    if(f == null || !f.exists()) return false;
     if (f.isDirectory()) {
       for (File sub : f.listFiles()) {
         if (!recurseDelete(sub)) {