it should be noted that an array with one or no elements works fine. for example:
<?php
 $a1 = array("1","2","3");
 $a2 = array("a");
 $a3 = array();
 
 echo "a1 is: '".implode("','",$a1)."'<br>";
 echo "a2 is: '".implode("','",$a2)."'<br>";
 echo "a3 is: '".implode("','",$a3)."'<br>";
?>

will produce:
===========
a1 is: '1','2','3'
a2 is: 'a'
a3 is: ''