src/Data/BizField.php
public function saveOldValue($value = null)
    {
        if ($value) {
            $this->oldValue = $value;
        } else {
            $this->oldValue = $this->value;
        }
    }
public function saveOldValue($value = null)
    {
        if ($value) {
            $this->oldValue = $value;
        } else {
            $this->oldValue = $this->value;
        }
    }
Save the old value to an internal variable

@param mixed $value
@return void