system/classes/Model.php
public function __isset($name)
    {
      // Get the calling class, so we can determine if isset was called internally or externally.
      $caller = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS, 2)[1]['class'];
      if ($caller == self::class) {
          return $this->getAttributeValue($name) != null;
      }
      return $this->getAttributeValueExtended($name) != null;
    }
public function __isset($name)
    {
      // Get the calling class, so we can determine if isset was called internally or externally.
      $caller = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS, 2)[1]['class'];
      if ($caller == self::class) {
          return $this->getAttributeValue($name) != null;
      }
      return $this->getAttributeValueExtended($name) != null;
    }
Within this model class, isset() is needed to check if things are set. Internally this needs to return false
for Cora extended class attributes.
However, outside this class, isset() can also be called, but in that case extended (using Cora extends system)
attributes need to return true.
In order to handle these opposite needed behaviors depending on who is calling, code was added to grab the calling class.