TextArray field type causes client JS errors

Expected behavior

1. No JS error when item is selected from Select field.
2. Additionally dependsOn working when set in TextArray field.

Actual/Current behavior

1. Error thrown: Uncaught TypeError: nextProps.value.join is not a function whenever item is selected from a Select field.
2. TextArray field does not appear when dependency met.

Steps to reproduce the actual/current behavior

TestList.add({
	selection: { type: Types.Select, initial: true, required: true, options: 'a,b,c' },
	items: { type: Types.TextArray, initial: true, dependsOn: { selection: 'b' } }
});

Environment

Software	Version
Keystone	4.0.0-beta.5
Node	8.2.1