title: A less cumbersome pattern for checking function parameters for nil in Clojure without throwing an assertion?
body: <p>This was asked <a href="https://stackoverflow.com/questions/22221645/is-there-a-quick-way-to-check-for-nil-args-in-a-clojure-function">here</a>, but the answers are all unacceptable.</p>
  
  <p>I'm trying to apply some defensive programming techniques to clojure and I'm finding some things cumbersome.</p>
  
  <p>Like checking function parameters:</p>
  
  <pre><code>(defn my-tolower [s]
    (if (nil? s) nil
                 (.toLowerCase s)
                 ))
  </code></pre>
  
  <p>Is there a cleaner way to do this?</p>
  
  <p>I'm aware of <code>:pre</code>, but that throws an exception.</p>