Methods with primitive args

[Nidroide]

server/main.js:

Meteor.methods({hello:(x)=>x});

shell:

curl -X POST http://localhost:3000/methods/hello -H "Content-type: application/json" -H "Accept: application/json" -d '"hello"'

server log:

W20170105-11:50:02.743(1)? (STDERR) Error: invalid json
W20170105-11:50:02.743(1)? (STDERR)     at parse (/home/nidroide/.meteor/packages/simple_json-routes/.2.1.0.9jn1dn++os+web.browser+web.cordova/npm/node_modules/connect/node_modules/body-parser/lib/types/json.js:83:15)
W20170105-11:50:02.743(1)? (STDERR)     at /home/nidroide/.meteor/packages/simple_json-routes/.2.1.0.9jn1dn++os+web.browser+web.cordova/npm/node_modules/connect/node_modules/body-parser/lib/read.js:108:18
W20170105-11:50:02.744(1)? (STDERR)     at invokeCallback (/home/nidroide/.meteor/packages/simple_json-routes/.2.1.0.9jn1dn++os+web.browser+web.cordova/npm/node_modules/connect/node_modules/body-parser/node_modules/raw-body/index.js:262:16)
W20170105-11:50:02.744(1)? (STDERR)     at done (/home/nidroide/.meteor/packages/simple_json-routes/.2.1.0.9jn1dn++os+web.browser+web.cordova/npm/node_modules/connect/node_modules/body-parser/node_modules/raw-body/index.js:251:7)
W20170105-11:50:02.744(1)? (STDERR)     at IncomingMessage.onEnd (/home/nidroide/.meteor/packages/simple_json-routes/.2.1.0.9jn1dn++os+web.browser+web.cordova/npm/node_modules/connect/node_modules/body-parser/node_modules/raw-body/index.js:308:7)
[...]

So how to call methods with primitive arguments? using method options and urlencoded arguments works but seems to be wasteful...anything am I missing?

note: per rfc 7159 "A JSON text is a sequence of tokens. The set of tokens includes six structural characters, strings, numbers, and three literal names. A JSON text is a serialized value. Note that certain previous specifications of JSON constrained a JSON text to be an object or an array."