title: check a string that contain only letter in asp.net
body: <p>why this code accept a null value ??? </p>
  
  <pre><code>protected bool ValidateOnlyLetter(String s)
      {
          if (String.IsNullOrEmpty(s)) return false;
          if (!Regex.IsMatch(s, "[\u0600-\u06ff]|[\u0750-\u077f]|[\ufb50-\ufc3f]|[\ufe70-\ufefc]") &amp;&amp; !Regex.IsMatch(s, "^[A-Za-z ]+$")) return false;
          return true;
      }
  </code></pre>
  
  <p>It's should accept only letter english or arabic but its accept empty string</p>
  
  <p>when I call the function : </p>
  
  <pre><code>if (!ValidateOnlyLetter(name.Text)) err1.Text = MessageNotification.Notify("Error");
  </code></pre>