title: What exception type should be thrown when trying to add duplicate items to a collection?
body: <p>Following code should throw exception to prevent adding duplicate collection item.</p>
  
  <pre><code>ICollection&lt;T&gt; collection = new List&lt;T&gt;();
  
  public void Add(T item)
  {
      if (collection.Contain(item))
      {
            throw new SomeExceptionType()
      }
  
      collection.Add(item);
  }
  </code></pre>
  
  <p>What standard exception type is the most appropriate?</p>