code: public <KEY extends Key<CoreMap, String>> String getString(Class<KEY> key) {
      String value = get(key);
      if (value == null) {
        return "";
      }
      return value;
    }
docs: Return a non-null String value for a key.
  This method is included for backwards compatibility with AbstractMapLabel.
  It is guaranteed to not return null; if the key is not present or
  has a null value, it returns the empty string ("").  It is only valid to
  call this method when key is paired with a value of type String.
  
  @param <KEY> A key type with a String value
  @param key The key to return the value of.
  @return "" if the key is not in the map or has the value <code>null</code>
  and the String value of the key otherwise