code: public static String concat(final Object... osToString) {
          final StringBuilder b = new StringBuilder();
          if (osToString != null) {
              for (final Object o : osToString) {
                  b.append(o != null ? o.toString() : "null");
              }
          }
          return b.toString();
      }
docs: Concatenate the string value of the objects (toString()). If osString is null, return empty ""
  but if one of the value is null, then use 'null' string.