Don't attempt to render features will null geometries in ol.render.canvas.Immediate
Don't attempt to render features will null geometries in ol.renderer.vector.renderFeature
Add extra assertion that feature's geometry is not null
Handle feature's geometries changing to and from null in ol.source.Vector
Merge pull request #1423 from twpayne/vector-api-null-geometries

[vector-api] Handle features with null geometries