Do not mix mapper types in JsonData serialization (#440) (#441)

Co-authored-by: Sylvain Wallez <sylvain@elastic.co>

java-client/src/main/java/co/elastic/clients/json/JsonDataImpl.java

@@ -108,9 +108,15 @@ public <T> T deserialize(JsonpDeserializer<T> deserializer, JsonpMapper mapper)
     public void serialize(JsonGenerator generator, JsonpMapper mapper) {
         if (value instanceof JsonValue) {
             generator.write((JsonValue) value);
+        } else if (this.mapper == null) {
+            mapper.serialize(value, generator);
+        } else if (this.mapper.getClass() != mapper.getClass()) {
+            // Workaround for https://github.com/elastic/elasticsearch-java/issues/424
+            // Mappers can require generators to have been created by them (see JacksonJsonpMapper), so use the mapper
+            // parameter if its class is different from the one passed at construction time.
+            mapper.serialize(value, generator);
         } else {
-            // Mapper provided at creation time has precedence
-            (this.mapper != null ? this.mapper : mapper).serialize(value, generator);
+            this.mapper.serialize(value, generator);
         }
     }