Only set content_type if it is sent back
Only set content_type if it is sent back

rdhyee/waterbutler,Johnetordoff/waterbutler,rafaeldelucena/waterbutler,TomBaxter/waterbutler,RCOSDP/waterbutler,kwierman/waterbutler,cosenal/waterbutler,icereval/waterbutler,chrisseto/waterbutler,felliott/waterbutler,CenterForOpenScience/waterbutler,Ghalko/waterbutler,hmoco/waterbutler