function checkType( type ) {
	if ( contains( FLOAT_TYPES, type ) ) {
		return true;
	}
	if ( contains( INTEGER_TYPES, type ) ) {
		return false;
	}
	return null;
}
Checks the return value type for whether return annotations should include a decimal point.

@private
@param {string} type - type name
@returns {(boolean|null)} for numbers, a boolean indicating whether return annotation value should include a decimal point, `null` otherwise