shouldSubscribe only works when propsToWatch is provided

[vladbalan]

It appears that shouldSubscribe only works as intended when propsToWatch is also provided in the options object, otherwise both currentProps and nextProps are equal to empty objects.

const options = {
  // propsToWatch: ['prop1', 'prop2', 'lastProp'],
  shouldSubscribe(currentProps, nextProps) {
    console.log('nextProps', nextProps); // returns {}
    console.log('currentProps', currentProps); // returns {}
  },
};

If propsToWatch is not provided, it defaults to null (https://github.com/arunoda/react-komposer/blob/a51a44de268587c1019ae834a95e24835fe23d85/src/compose.js#L14) and pick(props, null) === {} (https://github.com/arunoda/react-komposer/blob/a51a44de268587c1019ae834a95e24835fe23d85/src/compose.js#L59).