palantir/plottable — pull request #1336 by bluong (2014-11-15 00:02:55+00:00)
Title: [AbstractPlot] - Remove default x/y accessors

Having the default accessors right now forces us under the assumption of "is our accessor invalid or valid" rather than the easier, stricter assumption of "is our accessor null or valid". This is to move to the latter assumption.