antlr/antlr4 · error · IllegalArgumentException

pattern cannot be null

Error message

pattern cannot be null

What it means

Error "pattern cannot be null" thrown in antlr/antlr4.

Source

Thrown at runtime/Java/src/org/antlr/v4/runtime/tree/pattern/ParseTreeMatch.java:60

	 *
	 * @param tree The parse tree to match against the pattern.
	 * @param pattern The parse tree pattern.
	 * @param labels A mapping from label names to collections of
	 * {@link ParseTree} objects located by the tree pattern matching process.
	 * @param mismatchedNode The first node which failed to match the tree
	 * pattern during the matching process.
	 *
	 * @exception IllegalArgumentException if {@code tree} is {@code null}
	 * @exception IllegalArgumentException if {@code pattern} is {@code null}
	 * @exception IllegalArgumentException if {@code labels} is {@code null}
	 */
	public ParseTreeMatch(ParseTree tree, ParseTreePattern pattern, MultiMap<String, ParseTree> labels, ParseTree mismatchedNode) {
		if (tree == null) {
			throw new IllegalArgumentException("tree cannot be null");
		}

		if (pattern == null) {
			throw new IllegalArgumentException("pattern cannot be null");
		}

		if (labels == null) {
			throw new IllegalArgumentException("labels cannot be null");
		}

		this.tree = tree;
		this.pattern = pattern;
		this.labels = labels;
		this.mismatchedNode = mismatchedNode;
	}

	/**
	 * Get the last node associated with a specific {@code label}.
	 *
	 * <p>For example, for pattern {@code <id:ID>}, {@code get("id")} returns the
	 * node matched for that {@code ID}. If more than one node
	 * matched the specified label, only the last is returned. If there is

View on GitHub (pinned to 7d5770395b)

Solutions

1. Pass a non-null ParseTreePattern to the ParseTreeMatch constructor.
2. Obtain the pattern from ParseTreePatternMatcher.compile(...) and null-check it before use.

Example fix

ParseTreePattern pattern = matcher.compile("<expr>", ExprParser.RULE_expr);
if (pattern == null) throw new IllegalStateException("pattern compilation failed");
ParseTreeMatch match = pattern.match(tree);

When it happens

Trigger: ParseTreeMatch constructed with a null pattern argument.

Common situations: Ensure the ParseTreePattern from ParseTreePatternMatcher.compile() is non-null before creating a ParseTreeMatch.

AI-assisted analysis of antlr/antlr4@7d5770395b (2026-08-14). Data as JSON: /api/errors/0e672bc8680a5004. Report an issue: GitHub.