title: Insert null value to Sql server bigInt column
body: <p>A table contain bigInt column named 'Phone' I want to insert null value to this column by entity frame work. I used following codes:</p>
  
  <pre><code>objRegister.Phone = Convert.ToInt64(txtPhone.Text  ??null  );
  </code></pre>
  
  <p>But i get this message: "<code>Input string was not in a correct format.</code>".
  I change the code as shown in below:</p>
  
  <pre><code>objRegister.Phone = txtMobile.Text != null ?Convert.ToInt64(txtMobile.Text):((long?)null)  ;
  </code></pre>
  
  <p>I got same message : "<code>Input string was not in a correct format.</code>"</p>