Accessing anything under ruin.store of a ruin made from abandoned structures that did not have any storage before throws an exception from inside the API code. For now ruins of STRUCTURE_RAMPART, STRUCTURE_WALL, STRUCTURE_EXTRACTOR, and STRUCTURE_OBSERVER are confirmed to throw this errors.

Room: https://screeps.com/a/#!/room/shard1/E46S11

Structures that throw the exceptions: any of the ruins from outer rampart ring, ruins from extractor, and from observer.

Error in question:

TypeError: Cannot convert undefined or null to object
    at Function.entries (<anonymous>)
    at new <anonymous> (<runtime>:41413:16)
    at Object._storeGetter [as store] (<runtime>:41322:12)
    at Object.get [as store] (eval at exports.defineGameObjectProperties (<runtime>:1093:9), <anonymous>:7:61)
    at filter (role.builder:423:26)
    at arrayFilter (<runtime>:2665:13)
    at Function.filter (<runtime>:7590:14)
    at Object.find (<runtime>:14280:24)
    at Object.harvest (role.builder:420:32)

Code block throwing the exception:

    // look for ruins with stuff
    var ruins = creep.room.find(FIND_RUINS, {
        filter: function(r)
        {
            return r.store[RESOURCE_ENERGY] > 0;
        }
    });