ember-cli gives "Unexpected end of JSON input"

I have recent node (7.1.0) and npm (4.0.2) installations on macOS Sierra 10.12.1 with Xcode 8.1. The installation of the ember-cli package seems to work fine apart from two warnings:

08:51 $ npm install -g ember-cli
npm WARN deprecated node-uuid@1.4.7: use uuid module instead
npm WARN deprecated minimatch@2.0.10: Please update to minimatch 3.0.2 or higher to avoid a RegExp DoS issue
/usr/local/bin/ember -> /usr/local/lib/node_modules/ember-cli/bin/ember
/usr/local/lib
└── ember-cli@2.9.1 

But when I call ember it always gives me the following error:

08:52 $ ember --help
module.js:593
    throw err;
    ^

SyntaxError: /Users/torstenkemps-benedix/package.json: Unexpected end of JSON input
    at JSON.parse (<anonymous>)
    at Object.Module._extensions..json (module.js:590:27)
    at Module.load (module.js:490:32)
    at tryModuleLoad (module.js:449:12)
    at Function.Module._load (module.js:441:3)
    at Module.require (module.js:500:17)
    at require (internal/module.js:20:19)
    at Function.Project.getProjectRoot (/usr/local/lib/node_modules/ember-cli/lib/models/project.js:662:13)
    at module.exports (/usr/local/lib/node_modules/ember-cli/lib/cli/index.js:76:22)
    at /usr/local/lib/node_modules/ember-cli/bin/ember:27:3

How can I get ember to run correctly?