Updates the fields the body names, merged over the stored material: a key left out keeps its value and null clears it; translations (en/es/de/fr) merges per language. name is not writable here (use PUT) and, like any other unknown key, is ignored; an empty unit array is treated as not sent. Has the PUT's side effects — renames the raw-material product category, publishes the image, re-syncs the category into the style types. Responds with the record as GET /:id returns it. 404 material_not_found for an unknown id.