Using invalid iterator

Undefined behavior may result; the program may crash or subtly misbehave. An invalid or past-the-end iterator is being used
/src/mongo/s/write_ops/bulk_write_exec.cpp:189: INVALIDATE_ITERATOR 140504 Calling "find" with element "response.shardId" returns the end iterator.
/src/mongo/s/write_ops/bulk_write_exec.cpp:189: INVALIDATE_ITERATOR 140504 Assigning: "<temporary>" = "childBatches->find(response.shardId)".
/src/mongo/s/write_ops/bulk_write_exec.cpp:189: INVALIDATE_ITERATOR 140504 Dereferencing iterator "childBatches->find(response.shardId)" though it is already past the end of its container.