title: Why is the UpdateAsync method setting to null, false?
body: <p>I would like to update only EMAIL in the database.</p>
  <p>NOW field values in the database</p>
  <pre><code>Id = 1,
  Email = email@site.com,
  IsActiveSubscibe = true,
  PurchaseToken = &quot;sdsdsdsd&quot;,
  AutoRenewing = true,
  IsActiveSubscibe = true,
  DataTime = DateTime.UtcNow
  </code></pre>
  <p>doing UPDATE (I want to update only email)</p>
  <pre><code>Models.User user = new Models.User
  {
     Id = 1,
     Email = newEmail@site.com,
  
  };
    await App.Database.UpdateUser(user);
  </code></pre>
  <p>SQLITE METHOD</p>
  <pre><code>public Task UpdateUser(User user)
  {
    return database.UpdateAsync(user);
  }
  </code></pre>
  <p>After UPDATE. NOW field values in the database</p>
  <pre><code>Id = 1,
  Email = newEmail@site.com,
  IsActiveSubscibe = false,
  PurchaseToken = null,
  AutoRenewing = false
  IsActiveSubscibe = false,
  DataTime = null
  </code></pre>
  <p>The RESULT I would like to get</p>
  <pre><code>Id = 1,
  Email = newEmail@site.com,
  IsActiveSubscibe = true,
  PurchaseToken = &quot;sdsdsdsd&quot;,
  AutoRenewing = true,
  IsActiveSubscibe = true,
  DataTime = DateTime.UtcNow
  </code></pre>