BUG: Don't delete namespace if import fails.
BUG: Don't delete namespace if import fails.

datashape should be optional, this ensures it is actually optional.

bartosh/zipline,florentchandelier/zipline,quantopian/zipline,magne-max/zipline-ja,bartosh/zipline,enigmampc/catalyst,humdings/zipline,florentchandelier/zipline,magne-max/zipline-ja,alphaBenj/zipline,Scapogo/zipline,quantopian/zipline,Scapogo/zipline,alphaBenj/zipline,humdings/zipline,enigmampc/catalyst