code: public function getUnmappedKeys()
      {
          $u = [];
          $f = $this->unmappedForeignKeys;
          $l = $this->unmappedLocalKeys;
          if (!empty($f)) {
              $u['foreign'] = $f;
          }
          if (!empty($l)) {
              $u['local'] = $l;
          }
  
          return $u;
      }
docs: Get unmapped keys.
  
  @return [[@doctodo return_type:getUnmappedKeys]] [[@doctodo return_description:getUnmappedKeys]]