LUCENE-8130: fix NPE from TermStates.toString

lucene/CHANGES.txt

@@ -144,6 +144,8 @@ Bug Fixes
 
 * LUCENE-8120: Fix LatLonBoundingBox's toString() method (Martijn van Groningen, Adrien Grand)
 
+* LUCENE-8130: Fix NullPointerException from TermStates.toString() (Mike McCandless)
+
 Other
 
 * LUCENE-8111: IndexOrDocValuesQuery Javadoc references outdated method name.

lucene/core/src/java/org/apache/lucene/index/TermStates.java

@@ -224,7 +224,7 @@ public final class TermStates {
     sb.append("TermStates\n");
     for(TermState termState : states) {
       sb.append("  state=");
-      sb.append(termState.toString());
+      sb.append(termState);
       sb.append('\n');
     }
 

lucene/core/src/test/org/apache/lucene/index/TestTermStates.java

@@ -0,0 +1,36 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.lucene.index;
+
+import org.apache.lucene.document.Document;
+import org.apache.lucene.store.Directory;
+import org.apache.lucene.util.IOUtils;
+import org.apache.lucene.util.LuceneTestCase;
+
+public class TestTermStates extends LuceneTestCase {
+
+  public void testToStringOnNullTermState() throws Exception {
+    Directory dir = newDirectory();
+    RandomIndexWriter w = new RandomIndexWriter(random(), dir);
+    w.addDocument(new Document());
+    IndexReader r = w.getReader();
+    TermStates states = TermStates.build(r.getContext(), new Term("foo", "bar"), random().nextBoolean());
+    assertEquals("TermStates\n  state=null\n", states.toString());
+    IOUtils.close(r, w, dir);
+  }
+}