BUG: use get_dimension in case the image dimension is None
BUG: use get_dimension in case the image dimension is None

Former-commit-id: 620732f983e262847818474315c2611db7c4d689 [formerly 570b967c413f3b08f7366a4eb4bb1389ac93fd9b]
Former-commit-id: 8e0624d73902fd9b2677b4c80d1b391a019f2f6d
Former-commit-id: 8f1144f498df0c565e274118d8b4d1c130f0eb92
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox