[Demonstration 1]

[Buggy Method]
@Override
public CharSequence visitGroupStage(@NotNull MongoALParser.GroupStageContext ctx) {
    StringBuilder sb = new StringBuilder("{\"$group\":{");
    if (ctx.NOTHING() != null) {
        sb.append("\"_id\":null");
    } else {
        sb.append("\"_id\":").append(visit(ctx.addSubExpr()));
    }
    ListIterator<TerminalNode> simpleIds = ctx.SIMPLEID().listIterator();
    ListIterator<MongoALParser.AccumExprContext> accumExprs = ctx.accumExpr().listIterator();
    while (simpleIds.hasNext() && accumExprs.hasNext()) {
        sb.append(",\"").append(simpleIds.next().getText()).append("\":").append(accumExprs.next());
    }
    return sb.append("}}");
}

[Buggy Hunk]
.append(accumExprs.next());

[Patch]
.append(visit(accumExprs.next()));

[Demonstration 2]

[Buggy Method]
public String toJsonString() {
    StringBuilder sb = new StringBuilder("{\"time\":");
    sb.append(requestTime);
    sb.append(",\"duration\":");
    sb.append(duration);
    sb.append(",\"url\":\"");
    sb.append(url);
    sb.append("\",\"method\":\"");
    sb.append(method);
    sb.append('\"');
    sb.append(",\"status\":");
    sb.append(status);
    sb.append("\",\"contentType\":\"");
    sb.append(contentType);
    sb.append("\",");
    sb.append(getHeaders());
    sb.append(",");
    sb.append(getRequestHeaders());
    sb.append("}");
    return sb.toString();
}

[Buggy Hunk]
sb.append("\",\"contentType\":\"");

[Patch]
sb.append(",\"contentType\":\"");

[Demonstration 3]

[Buggy Method]
public static Result service(String ownerName, String projectName, String service, boolean isAdvertise) throws IOException, UnsupportedOperationException, ServletException {
    if (!isSupportedService(service)) {
        return forbidden(String.format("Unsupported service: '%s'", service));
    }
    Project project = Project.findByOwnerAndProjectName(ownerName, projectName);
    if (project == null) {
        return notFound();
    }
    models.User user = UserApp.currentUser();
    if (!isAllowed(project, service)) {
        if (user.isAnonymous()) {
            return BasicAuthAction.unauthorized(response());
        } else {
            // If you want the Git client showing your custom message to
            // the user, the Content-Type should be exact "text/plain"
            // without any parameter. For more details, see the code at
            // https://github.com/git/git/commit/426e70d4a11ce3b4f70636d57c6a0ab16ae08a00#diff-eea0ad565ec5903a11b6023755d491cfR154
            response().setHeader("Content-Type", "text/plain");
            return forbidden(String.format("'%s' has no permission to '%s/%s'.", user.name, ownerName, projectName));
        }
    }
    if (isAdvertise) {
        return ok(RepositoryService.gitAdvertise(project, service, response()));
    } else {
        if (request().body().isMaxSizeExceeded()) {
            return status(REQUEST_ENTITY_TOO_LARGE);
        } else {
            user.visits(project);
            return ok(RepositoryService.gitRpc(project, service, request(), response()));
        }
    }
}

[Buggy Hunk]
user.name, ownerName, projectName));

[Patch]
user.loginId, ownerName, projectName));