Reactives: invalid (NULL) left side of assignment
<p>I'm trying to extract an output of a personal function called tests.stats()</p>

<p>I make a function with <code>return</code> statement:</p>

<pre><code>   return(c(list.test.1, list.test.2 ,list.test.3, list.test.4))
</code></pre>

<p>Where each <code>list.test.&lt;i&gt;</code> is a <code>list</code> object.</p>

<p>In Shiny Server:</p>

<pre><code> outlist() &lt;- reactive({
   if(is.null(input$datafile)){
     return()
   }
   if(is.null(input$varinteret)
      &amp;&amp;is.null(input$vartemps)
      &amp;&amp;is.null(input$varsujet)
      &amp;&amp;is.null(input$varprod) 
      &amp;&amp;is.null(input$apparie)
      &amp;&amp;is.null(input$tempsrefouinon)
      &amp;&amp;is.null(input$prodrefouinon)
      &amp;&amp;is.null(input$checkprod)
      &amp;&amp;is.null(input$checkprodref)){
     return()
   } else {
     data&lt;-filedata()
     res &lt;- tests.stats(data = data(),
              y = input$varinteret, 
              group = input$varprod, 
              group2 = input$vartemps, 
              sujet = input$varsujet, 
              apparie = input$apparie, 
              temoin = input$prodrefouinon, 
              TemoinName = input$checkprodref)
   }  
</code></pre>

<p>and the error message:</p>

<pre><code>Warning: Error in &lt;-: invalid (NULL) left side of assignment
Stack trace (innermost first):
    40: server [C:\Users\itm\Desktop\Documents\appli/server.R#357]
     1: shiny::runApp
Error in outlist() &lt;- reactive({ : invalid (NULL) left side of assignment
</code></pre>

<p>Why am I receiving this error?</p>