code: public String putProperty(String key,
                                String value) {
          return this.getProperties().put(key,
                                          value);
      }
docs: changes an existing property with the same name, or adds a new one
  @param key property name with which the specified value is to be
  associated
  @param value value to be associated with the specified property name
  @return the previous value associated with property name, or null if
  there was no mapping for property name. (A null return can also
  indicate that the map previously associated null with key.)