Fix anaylze NullPointerException when AnalyzeTokenList tokens is null (#39332)

Author: weizijun

server/src/main/java/org/elasticsearch/action/admin/indices/analyze/DetailAnalyzeResponse.java

@@ -296,8 +296,10 @@ public static AnalyzeTokenList readAnalyzeTokenList(StreamInput in) throws IOExc
         XContentBuilder toXContentWithoutObject(XContentBuilder builder, Params params) throws IOException {
             builder.field(Fields.NAME, this.name);
             builder.startArray(AnalyzeResponse.Fields.TOKENS);
-            for (AnalyzeResponse.AnalyzeToken token : tokens) {
-                token.toXContent(builder, params);
+            if (tokens != null) {
+                for (AnalyzeResponse.AnalyzeToken token : tokens) {
+                    token.toXContent(builder, params);
+                }
             }
             builder.endArray();
             return builder;

server/src/test/java/org/elasticsearch/action/admin/indices/analyze/AnalyzeResponseTests.java

@@ -19,7 +19,12 @@
 
 package org.elasticsearch.action.admin.indices.analyze;
 
+import org.elasticsearch.common.bytes.BytesReference;
+import org.elasticsearch.common.xcontent.ToXContent;
+import org.elasticsearch.common.xcontent.XContentBuilder;
+import org.elasticsearch.common.xcontent.XContentHelper;
 import org.elasticsearch.common.xcontent.XContentParser;
+import org.elasticsearch.common.xcontent.json.JsonXContent;
 import org.elasticsearch.test.AbstractStreamableXContentTestCase;
 
 import java.io.IOException;
@@ -30,6 +35,8 @@
 import java.util.Map;
 import java.util.function.Predicate;
 
+import static org.hamcrest.Matchers.equalTo;
+
 public class AnalyzeResponseTests extends AbstractStreamableXContentTestCase<AnalyzeResponse> {
 
     @Override
@@ -112,4 +119,31 @@ private AnalyzeResponse.AnalyzeToken randomToken() {
         }
         return new AnalyzeResponse.AnalyzeToken(token, position, startOffset, endOffset, posLength, type, extras);
     }
+
+    public void testNullResponseToXContent() throws IOException {
+        DetailAnalyzeResponse.CharFilteredText[] charfilters = null;
+
+        String name = "test_tokens_null";
+        AnalyzeResponse.AnalyzeToken[] tokens = null;
+        DetailAnalyzeResponse.AnalyzeTokenList tokenizer = null;
+
+
+        DetailAnalyzeResponse.AnalyzeTokenList tokenfiltersItem = new DetailAnalyzeResponse.AnalyzeTokenList(name, tokens);
+        DetailAnalyzeResponse.AnalyzeTokenList[] tokenfilters = {tokenfiltersItem};
+
+        DetailAnalyzeResponse detail = new DetailAnalyzeResponse(charfilters, tokenizer, tokenfilters);
+
+        AnalyzeResponse response = new AnalyzeResponse(null, detail);
+        try (XContentBuilder builder = JsonXContent.contentBuilder()) {
+            response.toXContent(builder, ToXContent.EMPTY_PARAMS);
+            Map<String, Object> converted = XContentHelper.convertToMap(BytesReference.bytes(builder), false, builder.contentType()).v2();
+            List<Map<String, Object>> tokenfiltersValue = (List<Map<String, Object>>) ((Map<String, Object>)
+                converted.get("detail")).get("tokenfilters");
+            List<Map<String, Object>> nullTokens = (List<Map<String, Object>>) tokenfiltersValue.get(0).get("tokens");
+            String nameValue = (String) tokenfiltersValue.get(0).get("name");
+            assertThat(nullTokens.size(), equalTo(0));
+            assertThat(name, equalTo(nameValue));
+        }
+
+    }
 }