Merge branch 'ml-inference-unified-api-elastic' of github.com:elastic/elasticsearch into ml-inference-unified-api-elastic

Author: jonathan-buttner

server/src/main/java/org/elasticsearch/common/xcontent/ChunkedToXContentHelper.java

@@ -12,6 +12,7 @@
 import org.elasticsearch.common.collect.Iterators;
 import org.elasticsearch.xcontent.ToXContent;
 
+import java.util.Collections;
 import java.util.Iterator;
 
 public enum ChunkedToXContentHelper {
@@ -53,6 +54,14 @@ public static Iterator<ToXContent> field(String name, String value) {
         return Iterators.single(((builder, params) -> builder.field(name, value)));
     }
 
+    public static Iterator<ToXContent> optionalField(String name, String value) {
+        if (value == null) {
+            return Collections.emptyIterator();
+        } else {
+            return field(name, value);
+        }
+    }
+
     /**
      * Creates an Iterator of a single ToXContent object that serializes the given object as a single chunk. Just wraps {@link
      * Iterators#single}, but still useful because it avoids any type ambiguity.