Invalid argument supplied for foreach()

tl;dr

If you are trying to use a foreach loop, it's important to make sure that the argument you're supplying is valid.

Here's how to check if the argument is an array or an object:

if (is_array($values) || is_object($values))
{
    // Argument is valid, proceed with foreach loop
    foreach ($values as $value)
    {
        // Code to be executed in the loop
    }
}