code: function checkMethods(spec) {
    assert(spec.method, 'missing route methods');
  
    if (typeof spec.method === 'string') {
      spec.method = spec.method.split(' ');
    }
  
    if (!Array.isArray(spec.method)) {
      throw new TypeError('route methods must be an array or string');
    }
  
    if (spec.method.length === 0) {
      throw new Error('missing route method');
    }
  
    spec.method.forEach((method, i) => {
      assert(typeof method === 'string', 'route method must be a string');
      spec.method[i] = method.toLowerCase();
    });
  }
docs: Validate the spec.method
  
  @param {Object} spec
  @api private