title: Linq To Sql: Exception "String must be exactly one character long"
body: <p>Consider a SQL Server table defined with a <code>varchar(1) NULL</code> field. It's being used to store a gender character. Some rows have data, some not: either null or blank. Granted the blanks SHOULD be nulls, but consider that blank is a valid value here. I'd much prefer the value to be null.</p>
  
  <pre>
  ID    Gender
  1      'M'
  4      'M'
  3      ''
  4      'F'
  </pre>
  
  <p>An exception is raised when running a Linq To Sql query where the value of <code>someID</code> is 3.</p>
  
  <pre><code>var emp = (from e in db.Employees
             where e.ID == someID
             select e);
  </code></pre>
  
  <p><strong>Exception</strong>:</p>
  
  <blockquote>
    <p>String must be exactly one character long.</p>
  </blockquote>
  
  <p><strong>Question</strong>: What is the cause of this exception? What can be done to prevent or eliminate this problem?</p>