def dumpHierarchy(self, onlyVisibleNode):
raise NotImplementedError<EOL>
Return the json serializable dictionary holding the hierarchy data. Refer to sample of returned structure object
below.

Structure of the dict::

    {
        # name can be duplicated from the original name or just left the default one
        # if it cannot be determined, however providing some meaningful name is preferred
        'name': '<a recognizable string>'

        # All available attributes of this node are in form of key-value pairs
        'payload': {
            'name': '',
            'pos': [0, 0],
            'size': [1, 1],
            ...
        },

        # If there is no child, this part can be omitted
        'children': [
            {...},  # Same structure as this dict. 
        ],
    }

Returns:
    :obj:`dict` or :obj:`NoneType`: hierarchy data or None