Mixins cannot be properly removed via the REST Service

The existing REST service allows the update of mixins on a node, via the "PUT" method. However, when an update causes mixins to be removed, the following problems may occur:

• because the mixins are processed first (before any properties) it is impossible to remove a mixin if the node has properties defined which belong to that mixin or an ancestor of that mixin. This is because a validation is performed when removing the mixins which would result in a ConstraintViolationException
• the existing REST service doesn't handle properly removing of properties via update, by passing in null values or empty arrays. This is needed in order to be able to remove properties from a node.

Therefore, not only should the last point from above be implemented, but also the order in which mixins & properties are updated via the REST Service should be changed.