elastic/elasticsearch · error · IllegalArgumentException

invalid side: {}

Error message

invalid side: {}

What it means

Error "invalid side: {}" thrown in elastic/elasticsearch.

Source

Thrown at modules/analysis-common/src/main/java/org/elasticsearch/analysis/common/EdgeNGramTokenFilterFactory.java:56

        super(name);
        this.minGram = settings.getAsInt("min_gram", 1);
        this.maxGram = settings.getAsInt("max_gram", 2);
        if (settings.get("side") != null) {
            deprecationLogger.critical(
                DeprecationCategory.ANALYSIS,
                "edge_ngram_side_deprecated",
                "The [side] parameter is deprecated and will be removed. Use a [reverse] before and after the [edge_ngram] instead."
            );
        }
        this.side = parseSide(settings.get("side", "front"));
        this.preserveOriginal = settings.getAsBoolean(PRESERVE_ORIG_KEY, false);
    }

    static int parseSide(String side) {
        return switch (side) {
            case "front" -> SIDE_FRONT;
            case "back" -> SIDE_BACK;
            default -> throw new IllegalArgumentException("invalid side: " + side);
        };
    }

    @Override
    public TokenStream create(TokenStream tokenStream) {
        TokenStream result = tokenStream;

        // side=BACK is not supported anymore but applying ReverseStringFilter up-front and after the token filter has the same effect
        if (side == SIDE_BACK) {
            result = new ReverseStringFilter(result);
        }

        result = new EdgeNGramTokenFilter(result, minGram, maxGram, preserveOriginal);

        // side=BACK is not supported anymore but applying ReverseStringFilter up-front and after the token filter has the same effect
        if (side == SIDE_BACK) {
            result = new ReverseStringFilter(result);
        }

View on GitHub (pinned to db6a809a66)

When it happens

Trigger: Thrown at modules/analysis-common/src/main/java/org/elasticsearch/analysis/common/EdgeNGramTokenFilterFactory.java:56 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/026887d12da98c1f. Report an issue: GitHub.