code: public static void addValueIfNotNull( @Nonnull Map<String, String> parameters, @Nonnull String key, Object value ) {
          if( value == null ) {
              return;
          }
          parameters.put(key, value.toString());
      }
docs: Puts the given key/value into the given map only if the value is not null.
  
  @param parameters the map to add to
  @param key        the key of the value
  @param value      the value to add if not null