Object reference not set to an instance of an object strange behaviour with LINQ to SQL

Question

This is very bizarre.

The following code throws a Object reference not set to an instance of an object:

var members = db.Members.Where(
    a => 
        String.IsNullOrEmpty(searchEmail) 
            || (a.Email ?? "").ToUpper().Contains(searchEmail.ToUpper()));

where db is a DataContext and searchEmail is a string, which in this case is set to null.

The code should return all Members because the first half of the || returns true, however, I am getting the above exception.

Strangely if I change the code to:

var members = db.Members.Where(
    a => 
        String.IsNullOrEmpty(searchEmail) 
            || (a.Email ?? "").ToUpper().Contains((searchEmail ?? "").ToUpper()));

no exception is thrown! Presumably that means that String.IsNullOrEmpty is evaluating false when clearly it is evaluating true unless there is something about IQueryable's implementation of Where?

---

Update

Habib's answer is correct. For other people reading this, my solution to get around the limitation Habib explained was:

var members = db.Members.AsQueryable();

if (!String.IsNullOrEmpty(searchEmail))
    members = members.Where(a => a.Email.ToUpper()
                        .Contains(searchEmail.ToUpper()));

Answer 1

This LINQ expression translates in to SQL Query, it doesn't do short circuiting as expected. That is why you are getting th exception.

SQL-CLR Type Mismatches

C# specifies short circuit semantics based on lexical order of operands for logical operators && and ||. SQL on the other hand is targeted for set-based queries and therefore provides more freedom for the optimizer to decide the order of execution.