How to solve "implode(): Invalid arguments passed"?

Question

I'm trying to implode some checkbox values into a single String to store it on a Database field (as it is the only way I think I can do it), but I'm getting this error:

implode(): Invalid arguments passed

My HTML code is:

<input type="checkbox" name="oportunitats[]" value="1">
<input type="checkbox" name="oportunitats[]" value="2">
<input type="checkbox" name="oportunitats[]" value="3">
<input type="checkbox" name="oportunitats[]" value="4">

And my PHP looks like this:

$chk_oportunitats = implode(",",$_POST["oportunitats"]);

How can I fix this error?

Answer 1

The problem was I was checking $chk_oportunitats before any checkbox was selected, so the array was empty.

Solution PHP looks like this:

if (isset($_POST["oportunitats"])){
        $chk_oportunitats = implode(",",$_POST["oportunitats"]);
      }