src/Entity/Entity.php
public function getOldFieldValue($field)
    {
        return isset($this->old_values[$field]) ? $this->old_values[$field] : null;
    }
public function getOldFieldValue($field)
    {
        return isset($this->old_values[$field]) ? $this->old_values[$field] : null;
    }
Return all field value.

@param  string $field
@return mixed