Index: lucene/suggest/src/test/org/apache/lucene/search/suggest/analyzing/AnalyzingSuggesterTest.java
===================================================================
--- lucene/suggest/src/test/org/apache/lucene/search/suggest/analyzing/AnalyzingSuggesterTest.java	(revision 1495103)
+++ lucene/suggest/src/test/org/apache/lucene/search/suggest/analyzing/AnalyzingSuggesterTest.java	(working copy)
@@ -1164,4 +1164,33 @@
     assertEquals("[isla de muerta/8, i love lucy/7]", suggester.lookup("i", false, 3).toString());
     assertEquals("[i love lucy/7]", suggester.lookup("i ", false, 3).toString());
   }
+
+  public void testTooManyExpansions() throws Exception {
+
+    final Analyzer a = new Analyzer() {
+        @Override
+        protected TokenStreamComponents createComponents(String fieldName, Reader reader) {
+          Tokenizer tokenizer = new MockTokenizer(reader, MockTokenizer.SIMPLE, true);
+        
+          return new TokenStreamComponents(tokenizer) {
+            @Override
+            public TokenStream getTokenStream() {
+              Token a = new Token("a", 0, 1);
+              a.setPositionIncrement(1);
+              Token b = new Token("b", 0, 1);
+              b.setPositionIncrement(0);
+              return new CannedTokenStream(new Token[] {a, b});
+            }
+         
+            @Override
+            protected void setReader(final Reader reader) throws IOException {
+            }
+          };
+        }
+      };
+
+    AnalyzingSuggester suggester = new AnalyzingSuggester(a, a, 0, 256, 1);
+    suggester.build(new TermFreqArrayIterator(new TermFreq[] {new TermFreq("a", 1)}));
+    assertEquals("[a/1]", suggester.lookup("a", false, 1).toString());
+  }
 }
Index: lucene/CHANGES.txt
===================================================================
--- lucene/CHANGES.txt	(revision 1495103)
+++ lucene/CHANGES.txt	(working copy)
@@ -167,6 +167,9 @@
   when the sum of those shapes contain the query shape but none do individually.
   A flag was added to use the original faster algorithm. (David Smiley)
 
+* LUCENE-4971: Fixed NPE in AnalyzingSuggester when there are too many
+  graph expansions.  (Alexey Kudinov via Mike McCandless)
+
 Optimizations
 
 * LUCENE-4936: Improve numeric doc values compression in case all values share
Index: lucene/core/src/java/org/apache/lucene/util/automaton/SpecialOperations.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/util/automaton/SpecialOperations.java	(revision 1495103)
+++ lucene/core/src/java/org/apache/lucene/util/automaton/SpecialOperations.java	(working copy)
@@ -219,7 +219,7 @@
   /**
    * Returns the set of accepted strings, assuming that at most
    * <code>limit</code> strings are accepted. If more than <code>limit</code> 
-   * strings are accepted, null is returned. If <code>limit</code>&lt;0, then 
+   * strings are accepted, the first limit strings found are returned. If <code>limit</code>&lt;0, then 
    * the limit is infinite.
    */
   public static Set<IntsRef> getFiniteStrings(Automaton a, int limit) {
@@ -227,11 +227,9 @@
     if (a.isSingleton()) {
       if (limit > 0) {
         strings.add(Util.toUTF32(a.singleton, new IntsRef()));
-      } else {
-        return null;
       }
     } else if (!getFiniteStrings(a.initial, new HashSet<State>(), strings, new IntsRef(), limit)) {
-      return null;
+      return strings;
     }
     return strings;
   }