### Question:
RestUtils { public static <T> String makeS3CanonicalString(String method, String resource, Request<T> request, String expires) { return makeS3CanonicalString(method, resource, request, expires, null); }  static String makeS3CanonicalString(String method,
            String resource, Request<T> request, String expires); static String makeS3CanonicalString(String method,
            String resource, Request<T> request, String expires,
            Collection<String> additionalQueryParamsToSign);  }### Answer:
@Test public void testNullHeaderValue() { Request<?> request = new DefaultRequest<Object>("s3"); request.addHeader("x-amz-test", null); String canonicalString = RestUtils.makeS3CanonicalString( "PUT", "/bucket/key", request, null); Assert.assertEquals( "PUT\n\n\nx-amz-test:\n/bucket/key", canonicalString); }