title: R Readxl Error, EXPR must be a length 1 vector
body: <p>I am trying to load a .xls file on my mac using R studio Version 1.1.383</p>
  
  <pre><code>library(readxl);
  dataset &lt;- read_excel(NULL)
  Error in switch(ext, xls = "xls", xlsx = "xlsx", xlsm = "xlsx", if (nzchar(ext)) { :
  EXPR must be a length 1 vector
  </code></pre>
  
  <p>I read elsewhere on Stackoverflow that Switch expects a vector and so the issue is that I am trying to load a data frame but I could not find how to resolve.  I am not yet familiar with the contents of the xls file as it was sent to me to work on and I do not have Excel.</p>