System.Linq.Expressions.Expression.Coalesce C# (CSharp) Method

        public static BinaryExpression Coalesce(Expression left, Expression right, LambdaExpression conversion)
        {
            RequiresCanRead(left, nameof(left));
            RequiresCanRead(right, nameof(right));

            if (conversion == null)
            {
                Type resultType = ValidateCoalesceArgTypes(left.Type, right.Type);
                return new SimpleBinaryExpression(ExpressionType.Coalesce, left, right, resultType);
            }

            if (left.Type.GetTypeInfo().IsValueType && !left.Type.IsNullableType())
            {
                throw Error.CoalesceUsedOnNonNullType();
            }

            Type delegateType = conversion.Type;
            Debug.Assert(typeof(System.MulticastDelegate).IsAssignableFrom(delegateType) && delegateType != typeof(System.MulticastDelegate));
            MethodInfo method = delegateType.GetMethod("Invoke");
            if (method.ReturnType == typeof(void))
            {
                throw Error.UserDefinedOperatorMustNotBeVoid(conversion, nameof(conversion));
            }
            ParameterInfo[] pms = method.GetParametersCached();
            Debug.Assert(pms.Length == conversion.ParameterCount);
            if (pms.Length != 1)
            {
                throw Error.IncorrectNumberOfMethodCallArguments(conversion, nameof(conversion));
            }
            // The return type must match exactly.
            // We could weaken this restriction and
            // say that the return type must be assignable to from
            // the return type of the lambda.
            if (!TypeUtils.AreEquivalent(method.ReturnType, right.Type))
            {
                throw Error.OperandTypesDoNotMatchParameters(ExpressionType.Coalesce, conversion.ToString());
            }
            // The parameter of the conversion lambda must either be assignable
            // from the erased or unerased type of the left hand side.
            if (!ParameterIsAssignable(pms[0], left.Type.GetNonNullableType()) &&
                !ParameterIsAssignable(pms[0], left.Type))
            {
                throw Error.OperandTypesDoNotMatchParameters(ExpressionType.Coalesce, conversion.ToString());
            }
            return new CoalesceConversionBinaryExpression(left, right, conversion);
        }

        public void BinaryConversion()
        {
            var @object = typeof(object);
            var @null   =
                LinqExpression.Default(
                    @object);

            var expression =
                LinqExpression.Coalesce(
                    @null,
                    @null,
                    LinqExpression.Lambda(
                        @null,
                        LinqExpression.Parameter(
                            @object)));

            ShouldRoundrip(expression);
        }