.opts / .options warning raised when no options are set

When calling .opts on an element without passing any options a warning is emitted.

import holoviews as hv
hv.extension('bokeh')

hv.Scatter([0]).opts()

WARNING:param.main: Calling the .opts method with options broken down by options group (i.e. separate plot, style and norm groups) is deprecated. Use the .options method converting to the simplified format instead or use hv.opts.apply_groups for backward compatibility.

Users are unlikely to write that directly, but libraries like GeoViews use that in various places, for example: https://github.com/holoviz/geoviews/blob/master/geoviews/element/geo.py#L149-L150

[jlstevens]

As .opts.clear() exists already, the easiest thing is to do nothing when you have an empty.opts (so it is a no-op, without the warning).

[Hoxbro]

I noticed that an empty opts will reset previous options, this should not be the case in my opinion.