code: @Override
  	public boolean containsKey(final Object key) {
  		return propsMap.containsKey(key) ? true : defaults != null && defaults.containsKey(key);
  	}
docs: Return {@code true} if the property with the specified key exists. Defaults are considered in
  the result.
  
  @param key
  The key
  @return {@code true} if the property with the specified key exists