Index: CHANGES.txt
===================================================================
--- CHANGES.txt	(revision 960363)
+++ CHANGES.txt	(working copy)
@@ -474,6 +474,9 @@
   to wrap any other Analyzer and provide the same functionality as
   MaxFieldLength provided on IndexWriter.  This patch also fixes a bug
   in the offset calculation in CharTokenizer. (Uwe Schindler, Shai Erera)
+
+* LUCENE-2526: Don't throw NPE from MultiPhraseQuery.toString when
+  it's empty.  (Ross Woolf via Mike McCandless)
   
 Optimizations
 
Index: src/test/org/apache/lucene/search/TestMultiPhraseQuery.java
===================================================================
--- src/test/org/apache/lucene/search/TestMultiPhraseQuery.java	(revision 960363)
+++ src/test/org/apache/lucene/search/TestMultiPhraseQuery.java	(working copy)
@@ -263,4 +263,9 @@
     writer.addDocument(doc);
   }
 
+  // LUCENE-2526
+  public void testEmptyToString() {
+    new MultiPhraseQuery().toString();
+  }
+
 }
Index: src/java/org/apache/lucene/search/MultiPhraseQuery.java
===================================================================
--- src/java/org/apache/lucene/search/MultiPhraseQuery.java	(revision 960363)
+++ src/java/org/apache/lucene/search/MultiPhraseQuery.java	(working copy)
@@ -336,7 +336,7 @@
   @Override
   public final String toString(String f) {
     StringBuilder buffer = new StringBuilder();
-    if (!field.equals(f)) {
+    if (field == null || !field.equals(f)) {
       buffer.append(field);
       buffer.append(":");
     }