getAnnotations and clearAnnotations use different data structures for empty set.

[NodeGuy]

getAnnotations returns an array and clearAnnotations uses an object:

/**
* Returns the annotations for the `EditSession`.
* @returns {Object}
**/
this.getAnnotations = function() {
    return this.$annotations || [];
};

/**
* Clears all the annotations for this session. This function also triggers the `'changeAnnotation'` event.
**/
this.clearAnnotations = function() {
    this.$annotations = {};
    this._emit("changeAnnotation", {});
};

This causes an error when trying to add a single new annotation:

session.clearAnnotations();
session.setAnnotations(session.getAnnotations().concat(newAnnotation));

> TypeError: session.getAnnotations(...).concat is not a function

[NodeGuy]

Thanks for the super-fast fix! After creating the issue I decided to fix it myself, including writing a test case, before I saw your fix. Please consider including my pull request #1257 (rebased on top of your commit).