docs: public void setDefault(PropertyKey key, Object defaultValue) {
          if (null == defaultValue) {
              throw new IllegalArgumentException("defaultValue may not be null");
          }
          if (key.m_type != defaultValue.getClass()) {
              throw new IllegalArgumentException(
                      "defaultValue has wrong type, " +
                      "expected: " + key.m_type + ", found: " + 
                      defaultValue.getClass());
          }
          
          m_defaults.put(key, defaultValue);
      }