code: public static <T extends CharSequence> T checkArgNotNullOrEmpty(final T arg, final String argNameOrErrorMsg) {
          if (N.isNullOrEmpty(arg)) {
              if (argNameOrErrorMsg.indexOf(' ') == N.INDEX_NOT_FOUND) {
                  throw new IllegalArgumentException("'" + argNameOrErrorMsg + "' can not be null or empty");
              } else {
                  throw new IllegalArgumentException(argNameOrErrorMsg);
              }
          }
  
          return arg;
      }
docs: Checks if the specified {@code arg} is {@code null} or empty, and throws {@code IllegalArgumentException} if it is.
  
  @param arg
  @param argNameOrErrorMsg
  @throws IllegalArgumentException if the specified {@code arg} is {@code null} or empty.