object-position zeroes are not collapsible

[pydsigner]

>>> csscompressor.compress('img {object-position: 0 0;}')
'img{object-position:0}'

This looks right, but actually breaks the property, which is defined to use the same values as background-position: https://drafts.csswg.org/css-images/#the-object-position. However, background-position is actually handled correctly:

>>> csscompressor.compress('img {background-position: 0 0;}')
'img{background-position:0 0}'

[pydsigner]

A temporary workaround is to use synonyms for 0 0, like right top.