title: c# compiler error 'Parameter must be input safe. Invalid variance. The type parameter 'T' must be invariantly valid on Expression<TDelegate> '
body: <p>I want to use my interface co-variantly (Interface must be co-variant) but the Compiler give me error
  c# compiler error:- <strong>'Parameter must be input safe. Invalid variance. The type parameter 'T' must be invariantly valid on 'Expression'</strong> This is my code:</p>
  
  <pre><code>interface IRepository&lt;out T&gt; where T : BaseEntity
  {
      IEnumerable&lt;T&gt; Find(Expression&lt;Func&lt;T, bool&gt;&gt; predicate);
      T FindById(Guid id);
  }
  </code></pre>