A generalized store (Terminal, storage) will return the 'total' regardless, but most other objects will not. If you do not provide a RESOURCE_* (Where * is a resource) constant to the method, and it is a non-generalized store it will return null. You can use Object.keys() on the object's store property to retrieve the keys that are active, then check the amounts by looping though the keys and its store.

How can I tell what my creep/tombstone/container is storing? If you have made some new changes to you code and you suddenly find that all your creeps are the same role, likely when assigning, searching or checking the new role somewhere a = is suppose to be a = for example if your running logic for a creep if( = 'roleName') Will set every creep run, to the role name, instead of comparing.

27 Why is room.energyAvailable returning an incorrect number / why is my spawn not spawning a creep even though there's enough active extensions with energy for it?.

26 I purchased item(s) from Steam's Marketplace / Store (CPU Unlock, Access Key, Pixel,Decoration.) but can't find it in Screeps, where is it?.

25 Why can't I see my all my logs in the console? What's the limit?.

find() search against undefined not equivalent when nothing was found?

22 How can I stop my creep from blinking between rooms when attempting to move to a room?.

21 Why do I get an error when trying to access a reserved room and/or objects in a reserved room?.

20 Why won't RangeMassAttack() work on this Road/Wall/Container?.

19 Why wont my moveTo() / other creep methods work on the result of room.find()?.

18 Why won't my controller upgrade when its over its required progress total?.

17 Why is spawnCreep() giving me ERR_INVALID_ARGS as a return?.

16 Why isn't RESOURCES_ALL working to withdraw/transfer from this container/tombstone/creep?.

13 Why does findClosestByRange & Path not working?.

12 Why is my spawn not generating any more energy, shouldn't it generate to 300?.

11 Why is ansfer() returning an error when targeting my controller?.

10 Why is my creep not using exclusively roads with moveTo?.

9 Why is my game object in memory not working/updating?.

8 Why is getObjectByID() not returning an Object?.

7 Why can't I dismantle this InvaderCore!?.6 Why is my pathfinder path not working with moveByPath and/or not what I want?.5 Why is pathfinder pathing though my spawn/extension/tower?.3 Why is store.getXXX() returning Null?.2 How can I tell what my creep/tombstone/container is storing?.

Screeps doc