title: NULL value in designer-generated DataSet throws an exception I don't want
body: <p>I have a DataSet Designer in my project.</p>
  
  <p>One of my generated datasets has a column which can contain nulls. The database column itself can contain nulls. It's attached to the core table via a <code>LEFT OUTER JOIN</code> on another column which can, itself, contain nulls.</p>
  
  <p>The designer-generated code which results is this: </p>
  
  <pre><code>    &lt;Global.System.Diagnostics.DebuggerNonUserCodeAttribute(),  _
       Global.System.CodeDom.Compiler.GeneratedCodeAttribute("System.Data.Design.TypedDataSetGenerator", "4.0.0.0")&gt;  _
      Public Property DeptName() As String
          Get
              Try 
                  Return CType(Me(Me.tableEmployee.DeptNameColumn),String)
              Catch e As Global.System.InvalidCastException
                  Throw New Global.System.Data.StrongTypingException("The value for column 'DeptName' in table 'Employee' is DBNull.", e)
              End Try
          End Get
          Set
              Me(Me.tableEmployee.DeptNameColumn) = value
          End Set
      End Property
  </code></pre>
  
  <p>which throws an InvalidCastException when it sees a null. This is <strong>insane</strong>. Of <em>course</em> there'll be nulls. I'm expecting them. What I'm not expecting is exceptions being thrown <em>every time I check the data</em>.</p>
  
  <p>Is there any way to prompt the Designer to create a <code>String?</code> column instead of a <code>String</code> column? I mean, the column really should be nullable, to my way of thinking.</p>
  
  <p>I'm connecting to a SQL Server 9.0.50000 installation, which may or may not be relevant.</p>