feat: support customHash:null option
feat: support customHash:null option

joliss/broccoli-asset-rev,elucid/broccoli-asset-rev,dollarshaveclub/broccoli-asset-rev,rickharrison/broccoli-asset-rev,kevinlondon/broccoli-asset-rev,nadnoslen/broccoli-asset-rev,stefanpenner/broccoli-asset-rev