title: Check for unique item using when-validate-item
body: <p>I want to check my item to became unique in my database and the item exist in the databasemit must be clear(this item). </p>
  
  <p>So I use trigger when-validate-item for this item and trigger when-timer-expired for the form global.</p>
  
  <p>This is my code :</p>
  
  <p>//trigger when-Validate-item :</p>
  
  <pre><code>declare
    i number;    
    vTimer TIMER;
  begin
    IF //condition then
        i := show_alert('ERROR');    
        /* Create a timer with a 10 Millisecond delay */
        vTimer :=create_timer('TEMP',10,no_repeat);
    END IF;
  end;
  </code></pre>
  
  <p>//trigger when-timer-expired</p>
  
  <pre><code>GO_BLOCK ('name_block');    
  :name_block.item1:=NULL;
  DELETE_TIMER('TEMP');
  </code></pre>
  
  <p>But in runtime, I get this error:</p>
  
  <blockquote>
    <p>FRM-40202 Field must be entered</p>
  </blockquote>