message: Initialize array members of PolymerElement
diff: @@ -192,13 +192,13 @@ export interface PolymerExtension extends ElementBase {
  }
  export class PolymerElement extends Element implements PolymerExtension {
  - properties: PolymerProperty[];
  + properties: PolymerProperty[] = [];
  observers: {
  javascriptNode: estree.Expression | estree.SpreadElement,
  expression: LiteralValue
  - }[];
  - listeners: {event: string, handler: string}[];
  + }[] = [];
  + listeners: {event: string, handler: string}[] = [];
  behaviorAssignments: ScannedBehaviorAssignment[] = [];
  domModule?: dom5.Node;
  scriptElement?: dom5.Node;
  