title: fastshap: Error in UseMethod("explain") : no applicable method for 'explain' applied to an object of class "xgb.Booster"
body: <p>After fitting a xgboost model (model_n) I try to run the code below to obtain shap-values, where trainval is a dataframe with my traindata without the Y variabele:</p>
  <pre><code>shap_values &lt;- explain(model_n, X = trainval)
  </code></pre>
  <p>I receive this error:</p>
  <pre><code>[[Error in UseMethod(&quot;explain&quot;) : 
    no applicable method for 'explain' applied to an object of class [&quot;xgb.Booster&quot;]]
  </code></pre>
  <p>If I use this line:</p>
  <pre><code>shap_values &lt;- fastshap::explain(model_n, X = trainval)
  </code></pre>
  <p>I receive this error:</p>
  <pre><code>Error in explain.default(object, feature_names = feature_names, X = X,  : 
    argument &quot;pred_wrapper&quot; is missing, with no default
  </code></pre>
  <p>I have also tried with trainval as a matrix although this gives the same error.</p>
  <p>Any idea what could be the cause?</p>
  <p>Thanks a lot!</p>