code: public Signature getSignature(String email, String name) throws HelloSignException {
          if (email == null || "".equals(email)) {
              throw new HelloSignException("Email address cannot be empty");
          }
          if (name == null || "".equals(name)) {
              throw new HelloSignException("Name cannot be empty");
          }
          for (Signature s : getSignatures()) {
              if (email.equalsIgnoreCase(s.getEmail()) && name.equalsIgnoreCase(s.getName())) {
                  return s;
              }
          }
          return null;
      }
docs: Returns the signature for the given email/name combination, or null if
  not found on this request.
  
  @param email String email address
  @param name String name
  @return Signature or null if not found
  @throws HelloSignException if the email or name are empty