Wrap Expression in Expression.TryCatch

Question

I have some Expression<Func<T, bool>> exp and I need to write a method that would return new expression that represents the original one wrapped in try catch. For example, if original expression looks something like order => order.Product.Name == "Product 1" but order has no product, I need to return false instead of throwing exception;

Here is my method at the moment, but it throws runtime exception saying 'Expression of type 'System.Func2[MyClass,System.Boolean]' cannot be used for return type 'System.Boolean'`'

private static Expression<Func<T, bool>> FalseOnException<T>(this Expression<Func<T, bool>> exp)
{
    Expression<Func<T, bool>> falseExp = parameter => false;
    ParameterExpression parameter = exp.Parameters[0];
    var tryExp = Expression.TryCatch(exp, Expression.Catch(typeof(NullReferenceException), falseExp));
    return Expression.Lambda<Func<T, bool>>(tryExp.Body, parameter);
}

Where MyClass is T

Answer 1

We can adapt the example from the docs a little and it will work:

Expression<Func<T, bool>> FalseOnNullReferenceException<T>(Expression<Func<T, bool>> exp) {

    var parameterExpression = Expression.Parameter(typeof(T));
    TryExpression tryCatchExpr =
        Expression.TryCatch(
                Expression.Invoke(exp, parameterExpression)
            ,
            Expression.Catch(
                typeof(NullReferenceException),
                Expression.Constant(false, typeof(bool))
            )
        );
    return Expression.Lambda<Func<T, bool>>(tryCatchExpr, parameterExpression);;

}

Quick test:

class Foo {
    public string Bar { get; set; }
}

Expression<Func<Foo, bool>> exp = f => f.Bar == "Baz";

//exp.Compile()(null); // throws

var tryCatchExp = FalseOnNullReferenceException(exp);

var compiled = tryCatchExp.Compile();
var foo = new Foo { Bar = "Baz" };
Console.WriteLine(compiled(null)); // false
Console.WriteLine(compiled(foo)); // true