Ransack sort Nested Assosiation on attribute name
<p>I have a model named <code>Project</code> with this association set up to link employees as contributors:</p>

<pre><code>has_many :project_contributions,  dependent: :destroy
has_many :contributors, through: :project_contributions, source: 'employee'
</code></pre>

<p>In my view i have this sort field:</p>

<pre><code>&lt;%= sort_link(@q, :contributors_name) %&gt;
</code></pre>

<p>This gives me an error when i click the link, it's complaining that the method does not exist. </p>

<p>I can see that since the association is a <code>has_many</code> association i should "name" the sort link something else, but i have no clue what i should be. </p>

<p>Or does Ransack not support has_many sorting? Also it might be that i use a different name that the original table name (<code>employee</code>).</p>

<p><strong>Update:</strong> I have discovered that the bug is related to the fact that i have changed the order function to make null values appear last when sorting. Like i show in this answer: 
<a href="https://stackoverflow.com/a/35529699/900271">https://stackoverflow.com/a/35529699/900271</a></p>

<p>Does any one know how i can allow nested column sorting while still ordering null values last?</p>