Make setting image rotation and subtractViewRotation optional

src/objectliterals.jsdoc

@@ -628,11 +628,11 @@
  * @typedef {Object} ol.style.ImageOptions
  * @property {ol.Pixel} anchor Anchor.
  * @property {HTMLCanvasElement|HTMLVideoElement|Image} image Image.
- * @property {number} rotation Rotation.
+ * @property {number|undefined} rotation Rotation.
  * @property {ol.Size} size Image size in pixel.
  * @property {boolean|undefined} snapToPixel Whether the image should be
  *     snapped to the closed pixel at rendering time.
- * @property {boolean} subtractViewRotation Whether the image should be
+ * @property {boolean|undefined} subtractViewRotation Whether the image should be
  *     rotated with the view or not.
  */
 

src/ol/style/imagestyle.js

@@ -21,7 +21,7 @@ ol.style.Image = function(options) {
   this.image = options.image;
 
   /**
-   * @type {number}
+   * @type {number|undefined}
    */
   this.rotation = options.rotation;
 
@@ -36,7 +36,7 @@ ol.style.Image = function(options) {
   this.snapToPixel = options.snapToPixel;
 
   /**
-   * @type {boolean}
+   * @type {boolean|undefined}
    */
   this.subtractViewRotation = options.subtractViewRotation;