Fix BWC issue

Author: przemekwitek

docs/reference/query-languages/esql/_snippets/functions/parameters/bucket.md

@@ -323,6 +323,7 @@ static TransportVersion def(int id) {
     public static final TransportVersion ML_INFERENCE_ELASTIC_DENSE_TEXT_EMBEDDINGS_ADDED = def(9_109_00_0);
     public static final TransportVersion ML_INFERENCE_COHERE_API_VERSION = def(9_110_0_00);
     public static final TransportVersion ESQL_PROFILE_INCLUDE_PLAN = def(9_111_0_00);
+    public static final TransportVersion ESQL_EMIT_EMPTY_BUCKETS = def(9_112_0_00);
 
     /*
      * STOP! READ THIS FIRST! No, really,

docs/reference/query-languages/esql/_snippets/functions/types/bucket.md

@@ -8,6 +8,7 @@
 package org.elasticsearch.xpack.esql.expression.function.grouping;
 
 import org.apache.lucene.util.BytesRef;
+import org.elasticsearch.TransportVersions;
 import org.elasticsearch.common.Rounding;
 import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
 import org.elasticsearch.common.io.stream.StreamInput;
@@ -235,8 +236,10 @@ private Bucket(StreamInput in) throws IOException {
             in.readNamedWriteable(Expression.class),
             in.readOptionalNamedWriteable(Expression.class),
             in.readOptionalNamedWriteable(Expression.class),
-            in.readOptionalNamedWriteable(Expression.class)
-        );
+            in.getTransportVersion().onOrAfter(TransportVersions.ESQL_EMIT_EMPTY_BUCKETS)
+                ? in.readOptionalNamedWriteable(Expression.class)
+                : null
+            );
     }
 
     private static List<Expression> fields(Expression field, Expression buckets, Expression from, Expression to, Expression emitEmptyBuckets) {
@@ -262,7 +265,9 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeNamedWriteable(buckets);
         out.writeOptionalNamedWriteable(from);
         out.writeOptionalNamedWriteable(to);
-        out.writeOptionalNamedWriteable(emitEmptyBuckets);
+        if (out.getTransportVersion().onOrAfter(TransportVersions.ESQL_EMIT_EMPTY_BUCKETS)) {
+            out.writeOptionalNamedWriteable(emitEmptyBuckets);
+        }
     }
 
     @Override