code: public static String setOrAppend(final String target, final String value, final boolean withSpace) {
          if (target == null) {
              return value;
          }if(value == null) {
              return target;
          } else {
              if (withSpace && !target.endsWith(STRING_BLANK)) {
                  return target + STRING_BLANK + value;
              } else {
                  return target + value;
              }
          }
      }
docs: If target is null, return the value; else append value to target.
  If withSpace is true, insert a blank between them.
  @param target target to be appended
  @param value value to append
  @param withSpace whether insert a blank
  @return processed string