code: function (changes, cb) {
          var okKeys = {
              sid: true,
              action: true,
              initiator: true,
              responder: true
          };
  
          var unknownPayload = false;
          Object.keys(changes).forEach(function (key) {
              if (!okKeys[key]) {
                  unknownPayload = true;
              }
          });
  
          if (unknownPayload) {
              cb({
                  type: 'modify',
                  condition: 'feature-not-implemented',
                  jingleCondition: 'unsupported-info'
              });
          } else {
              cb();
          }
      }
docs: It is mandatory to reply to a session-info action with an unsupported-info error if the info isn't recognized.  However, a session-info action with no associated payload is acceptable (works like a ping).