code: @Nullable
    public String getProperty (@Nullable final String sKey, @Nullable final String sDefaultValue)
    {
      final String sValue = getProperty (sKey);
      return sValue == null ? sDefaultValue : sValue;
    }
docs: Searches for the property with the specified key in this property list. If
  the key is not found in this property list, the default property list, and
  its defaults, recursively, are then checked. The method returns the default
  value argument if the property is not found.
  
  @param sKey
  the map key.
  @param sDefaultValue
  a default value.
  @return the value in this property list with the specified key value.
  @see #setProperty