code: private ParseTree parseUnaryExpression() {
      SourcePosition start = getTreeStartLocation();
      if (peekUnaryOperator()) {
        Token operator = nextToken();
        ParseTree operand = parseUnaryExpression();
        return new UnaryExpressionTree(getTreeLocation(start), operator, operand);
      } else if (peekAwaitExpression()) {
        return parseAwaitExpression();
      } else {
        return parseUpdateExpression();
      }
    }
docs: 11.4 Unary Operator