title: Handling empty strings in string detection
body: <p>I would like to use str_detect and not convert "" to another string pattern.  Is there an easy way to deal with empty string patterns "" which right now generates a warning.  I would like this to produce TRUE, FALSE, FALSE, FALSE, FALSE</p>
  
  <pre><code>library( tidyverse )
  str_detect('matt', c( "matt","joe","liz","", NA))
  </code></pre>