Illegal type for source – How to solve this Elasticsearch exception

Opster Team

August-23, Version: 6.8-8.9

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Briefly, this error occurs when the _source field in Elasticsearch is assigned an illegal type, such as an empty object. The _source field should contain the original JSON document that was indexed. To resolve this issue, ensure that the _source field is assigned a valid JSON document. If you’re not using the _source field, you can disable it in the index settings. However, be aware that this will prevent you from being able to reindex data or use certain features like highlighting.

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This guide will help you check for common problems that cause the log ” illegal type for _source: [{}] ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: .

Log Context

Log “illegal type for _source: [{}]” class name is We extracted the following from Elasticsearch source code for those seeking an in-depth context :

 fetchSourceContext == null || fetchSourceContext.fetchSource();
 new String[] { parser.text() };
 fetchSourceContext == null ? Strings.EMPTY_ARRAY : fetchSourceContext.excludes()
 } else {
 throw new ElasticsearchParseException("illegal type for _source: [{}]"; token);
 } else {
 throw new ElasticsearchParseException(
 "failed to parse multi get request. unknown field [{}]";


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