docs: private static int isAlwaysDefinedBoolean(Node node) {
          switch (node.getType()) {
            case Token.FALSE:
            case Token.NULL:
              return ALWAYS_FALSE_BOOLEAN;
            case Token.TRUE:
              return ALWAYS_TRUE_BOOLEAN;
            case Token.NUMBER: {
              double num = node.getDouble();
              if (num == num && num != 0.0) {
                  return ALWAYS_TRUE_BOOLEAN;
              }
              return ALWAYS_FALSE_BOOLEAN;
            }
          }
          return 0;
      }