Regression: can-diff/list/ causes can-reflect.getSchema to throw an error

[chasenlehara]

[This is arguably a bug in can-reflect, but since can-diff is what changed recently, filing it here.]

This code is new in can-diff:

can-diff/list/list.js

Lines 43 to 45 in bb2fb96

	if(typeSchema == null && oldListLength > 0) {
	typeSchema = canReflect.getSchema( canReflect.getKeyValue(oldList, 0) );
	}

One might expect that if oldListLength > 0, then oldListLength[0] would be present… but this isn’t always the case. 😅

I’m not 100% sure what code is responsible for making the list, but oldList is an array with objects at various indices, not including [0], so that line passes undefined to can-reflect.getSchema, which throws here: https://github.com/canjs/can-reflect/blob/339f55666ce3101482e5d3fc3262a7626ae6e63a/reflections/shape/schema/schema.js#L106

If need be, I’m happy to pair on this to show it in a real project.

[justinbmeyer]

getSchema should probably return undefined if undefined is passed.