REST does not return alternate chars. Some chars are missing

I am trying to take a string as input from rest client and return json with alternate chars. However, some chars are missing from the string when it returns. On console, all the chars are getting printed.

@Path("/person")
public class PersonResource {

    @GET
    @Produces("application/json")

    @Path("/{userid}")
    public Response getJson(@PathParam("userid") String userId) {

        return Response.ok(test(userId)).build();
    }

    public String test(String userId) {

        if (userId.length() == 0) {
            System.out.println("Enter User name");
        }
        System.out.println(userId);
        char[] c = userId.toCharArray();

        userId = "";
        for (int i = 0; i < c.length; i=i+2) {
            System.out.println(Character.toString(c[i]) + " "  + i );
            if ((int) c[i] > 127) {
                return "invalid chars";
            } else if (c[i] % 2 == 0) {
                userId = userId + Character.toString(c[i]);
            }
        }

The request from REST client is

http://localhost:8084/JSONProjectTest/api/person/HelloWorld

and

REST Client returns Hll.json

On console, the following prints:

HelloWorld
H 0
l 2
o 4
o 6
l 8

I tried changing the decimal of chars, but nothing comes up.