Allow some units to not define return_units
Allow some units to not define return_units

saimn/astropy,astropy/astropy,larrybradley/astropy,lpsinger/astropy,aleksandr-bakanov/astropy,mhvk/astropy,mhvk/astropy,saimn/astropy,lpsinger/astropy,larrybradley/astropy,bsipocz/astropy,StuartLittlefair/astropy,astropy/astropy,astropy/astropy,MSeifert04/astropy,aleksandr-bakanov/astropy,saimn/astropy,pllim/astropy,aleksandr-bakanov/astropy,pllim/astropy,dhomeier/astropy,lpsinger/astropy,mhvk/astropy,bsipocz/astropy,MSeifert04/astropy,larrybradley/astropy,saimn/astropy,lpsinger/astropy,StuartLittlefair/astropy,stargaser/astropy,MSeifert04/astropy,pllim/astropy,dhomeier/astropy,bsipocz/astropy,dhomeier/astropy,pllim/astropy,stargaser/astropy,aleksandr-bakanov/astropy,larrybradley/astropy,dhomeier/astropy,StuartLittlefair/astropy,StuartLittlefair/astropy,MSeifert04/astropy,lpsinger/astropy,pllim/astropy,mhvk/astropy,astropy/astropy,saimn/astropy,dhomeier/astropy,StuartLittlefair/astropy,astropy/astropy,bsipocz/astropy,stargaser/astropy,mhvk/astropy,stargaser/astropy,larrybradley/astropy