Falsey keys for attributes don't render colors correctly

[wparad]

If you set the key of the attribute for a date range to be 0, it doesn't render the specified colors.

Example:

const attributes = [
{ key: 0, highlight: 'red', dates: new Date(Date.now() - 86400000) },
{ key1: highlight: 'blue', dates: new Date() }
}];

Correct: