/// <summary>
        /// Reads a null condition expression from the code.
        /// </summary>
        /// <param name="leftHandSide">The left hand side.</param>
        /// <param name="previousPrecedence">The previous precedence.</param>
        /// <param name="parentReference">The parent code unit.</param>
        /// <param name="unsafeCode">Indicates whether the code being parsed resides in an unsafe code block.</param>
        /// <returns>
        /// Returns the expression.
        /// </returns>
        private Expression GetNullConditionExpression(
            Expression leftHandSide, ExpressionPrecedence previousPrecedence, Reference<ICodePart> parentReference, bool unsafeCode)
        {
            Param.AssertNotNull(leftHandSide, "leftHandSide");
            Param.Ignore(previousPrecedence);
            Param.AssertNotNull(parentReference, "parentReference");
            Param.Ignore(unsafeCode);

            NullConditionExpression expression = null;
            Reference<ICodePart> expressionReference = new Reference<ICodePart>();

            // Read the details of the expression.
            OperatorSymbol operatorToken = this.PeekOperatorToken(parentReference, expressionReference);
            Debug.Assert(operatorToken.SymbolType == OperatorType.NullConditional, "Expected a null-conditional symbol");

            // Check the precedence of the operators to make sure we can gather this statement now.
            ExpressionPrecedence precedence = GetOperatorPrecedence(operatorToken.SymbolType);
            if (CheckPrecedence(previousPrecedence, precedence))
            {
                // Add the operator token to the document and advance the symbol manager up to it.
                this.symbols.Advance();
                this.tokens.Add(operatorToken);

                Expression rightHandSide = null;
                Symbol nextSymbol = this.symbols.Peek(1);

                // Check if next symbol is an open square bracket.
                if (nextSymbol.SymbolType == SymbolType.OpenSquareBracket)
                {
                    rightHandSide = this.GetArrayAccessExpression(leftHandSide, previousPrecedence, unsafeCode);
                }
                else
                {
                    rightHandSide = this.GetOperatorRightHandExpression(precedence, expressionReference, unsafeCode);
                }

                // We must find an expression else there is a syntax exception.
                if (rightHandSide == null)
                {
                    this.CreateSyntaxException();
                }

                // Create the partial token list for the expression.
                CsTokenList partialTokens = new CsTokenList(this.tokens, leftHandSide.Tokens.First, this.tokens.Last);

                // Create and return the expression.
                expression = new NullConditionExpression(partialTokens, leftHandSide, rightHandSide);
                expressionReference.Target = expression;
            }

            return expression;
        }
        /// <summary>
        /// Reads a null condition expression from the code.
        /// </summary>
        /// <param name="leftHandSide">The left hand side.</param>
        /// <param name="previousPrecedence">The previous precedence.</param>
        /// <param name="parentReference">The parent code unit.</param>
        /// <param name="unsafeCode">Indicates whether the code being parsed resides in an unsafe code block.</param>
        /// <returns>
        /// Returns the expression.
        /// </returns>
        private Expression GetNullConditionExpression(
            Expression leftHandSide, ExpressionPrecedence previousPrecedence, Reference<ICodePart> parentReference, bool unsafeCode)
        {
            Param.AssertNotNull(leftHandSide, "leftHandSide");
            Param.Ignore(previousPrecedence);
            Param.AssertNotNull(parentReference, "parentReference");
            Param.Ignore(unsafeCode);

            NullConditionExpression expression = null;
            Reference<ICodePart> expressionReference = new Reference<ICodePart>();

            // Read the details of the expression.
            OperatorSymbol operatorToken = this.PeekOperatorToken(parentReference, expressionReference);
            Debug.Assert(operatorToken.SymbolType == OperatorType.NullConditional, "Expected a null-conditional symbol");

            // Check the precedence of the operators to make sure we can gather this statement now.
            ExpressionPrecedence precedence = GetOperatorPrecedence(operatorToken.SymbolType);
            if (CheckPrecedence(previousPrecedence, precedence))
            {
                // Add the operator token to the document and advance the symbol manager up to it.
                this.symbols.Advance();
                this.tokens.Add(operatorToken);

                // Get the expression on the right-hand side of the operator.
                Expression rightHandSide = this.GetOperatorRightHandExpression(precedence, expressionReference, unsafeCode);

                // Create the partial token list for the expression.
                CsTokenList partialTokens = new CsTokenList(this.tokens, leftHandSide.Tokens.First, this.tokens.Last);

                // Create and return the expression.
                expression = new NullConditionExpression(partialTokens, leftHandSide, rightHandSide);
                expressionReference.Target = expression;
            }

            return expression;
        }