title: bind_param Number of variables doesn't match number of parameters in prepared statement
body: <p>Here is a snippet from my code:</p>
  <pre><code>$stmt = $mysqli-&gt;prepare(&quot;SELECT DISTINCT model FROM vehicle_types 
      WHERE year = ? AND make = '?' ORDER by model&quot;);
  
  $stmt-&gt;bind_param('is', $year, $make);
  
  $stmt-&gt;execute();
  </code></pre>
  <p>When I echo out the values for $year and $make, I am seeing values, but when I run this script, I get a null value, and the following warning appears in my log file:</p>
  <blockquote>
  <p>PHP Warning:  mysqli_stmt::bind_param(): Number of variables doesn't match number of parameters in prepared statement</p>
  </blockquote>
  <p>In this case, year is in the database in type int(10), and I have tried passing a copy that had been cast as an int, and make is a varchar(20) with the utf8_unicode_ci encoding. Am I missing something?</p>