java-symbol-solver-core/src/main/java/com/github/javaparser/symbolsolver/javaparsermodel/JavaParserFacade.java
private Optional<ResolvedType> find(Map<Node, ResolvedType> map, LambdaExpr lambdaExpr) {
        for (Node key : map.keySet()) {
            if (key instanceof LambdaExpr) {
                LambdaExpr keyLambdaExpr = (LambdaExpr) key;
                if (keyLambdaExpr.toString().equals(lambdaExpr.toString()) && getParentNode(keyLambdaExpr) == getParentNode(lambdaExpr)) {
                    return Optional.of(map.get(keyLambdaExpr));
                }
            }
        }
        return Optional.empty();
    }
private Optional<ResolvedType> find(Map<Node, ResolvedType> map, LambdaExpr lambdaExpr) {
        for (Node key : map.keySet()) {
            if (key instanceof LambdaExpr) {
                LambdaExpr keyLambdaExpr = (LambdaExpr) key;
                if (keyLambdaExpr.toString().equals(lambdaExpr.toString()) && getParentNode(keyLambdaExpr) == getParentNode(lambdaExpr)) {
                    return Optional.of(map.get(keyLambdaExpr));
                }
            }
        }
        return Optional.empty();
    }
For some reasons LambdaExprs are duplicate and the equals method is not implemented correctly.

@param map
@return