code: public static Class<?> wrap(final Class<?> cls) {
          N.checkArgNotNull(cls, "cls");
  
          final Class<?> wrapped = PRIMITIVE_2_WRAPPER.get(cls);
  
          return wrapped == null ? cls : wrapped;
      }
docs: Returns the corresponding wrapper type of {@code type} if it is a primitive type; otherwise
  returns {@code type} itself. Idempotent.
  
  <pre>
  wrap(int.class) == Integer.class
  wrap(Integer.class) == Integer.class
  wrap(String.class) == String.class
  </pre>