Fetch fields parameter must not be empty – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 8.2-8.9

Briefly, this error occurs when the [fetch_fields] parameter in an Elasticsearch query is left empty. This parameter is used to specify which fields should be returned in the response. If it’s empty, Elasticsearch doesn’t know which fields to fetch. To resolve this issue, you can either specify the fields you want to fetch in the [fetch_fields] parameter or remove the parameter entirely if you want all fields to be returned.

This guide will help you check for common problems that cause the log ” [fetch_fields] parameter must not be empty ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: index.

Log Context

Log “[fetch_fields] parameter must not be empty” class name is LookupRuntimeFieldType.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 fetchFields.addValidator(fields -> {
 if (fields.isEmpty()) {
 throw new MapperParsingException("[fetch_fields] parameter must not be empty");
 return fetchFields;


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