elastic/elasticsearch · error · IllegalArgumentException

stemmer override filter requires either `rules` or `rules_pa

Error message

stemmer override filter requires either `rules` or `rules_path` to be configured

What it means

Error "stemmer override filter requires either `rules` or `rules_path` to be configured" thrown in elastic/elasticsearch.

Source

Thrown at modules/analysis-common/src/main/java/org/elasticsearch/analysis/common/StemmerOverrideTokenFilterFactory.java:33

import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.env.Environment;
import org.elasticsearch.index.IndexSettings;
import org.elasticsearch.index.analysis.AbstractTokenFilterFactory;
import org.elasticsearch.index.analysis.Analysis;

import java.io.IOException;
import java.util.List;

public class StemmerOverrideTokenFilterFactory extends AbstractTokenFilterFactory {

    private final StemmerOverrideMap overrideMap;

    StemmerOverrideTokenFilterFactory(IndexSettings indexSettings, Environment env, String name, Settings settings) throws IOException {
        super(name);

        List<String> rules = Analysis.getWordList(env, settings, "rules");
        if (rules == null) {
            throw new IllegalArgumentException("stemmer override filter requires either `rules` or `rules_path` to be configured");
        }

        StemmerOverrideFilter.Builder builder = new StemmerOverrideFilter.Builder(false);
        parseRules(rules, builder, "=>");
        overrideMap = builder.build();

    }

    @Override
    public TokenStream create(TokenStream tokenStream) {
        return new StemmerOverrideFilter(tokenStream, overrideMap);
    }

    static void parseRules(List<String> rules, StemmerOverrideFilter.Builder builder, String mappingSep) {
        for (String rule : rules) {
            String[] sides = rule.split(mappingSep, -1);
            if (sides.length != 2) {
                throw new RuntimeException("Invalid Keyword override Rule:" + rule);

View on GitHub (pinned to db6a809a66)

When it happens

Trigger: Thrown at modules/analysis-common/src/main/java/org/elasticsearch/analysis/common/StemmerOverrideTokenFilterFactory.java:33 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of elastic/elasticsearch@db6a809a66 (2026-08-12). Data as JSON: /api/errors/ebdf44bf730c1fc4. Report an issue: GitHub.