Performance::GenerateResourceTiming calls GetResourceLoadTiming() and often assumed it to be never be null. But it seems that this can return null. We should investigate why this is happening and either returning null is a bug and must be fixed, OR returning null is reasonable and the code must always be surrounded with if statements when the output 
from GetResourceLoadTiming() is used.
 

Performance::GenerateResourceTiming calls GetResourceLoadTiming() and often assumes that the output is not null. But it seems that this can return null. We should investigate why this is happening and either returning null is a bug and must be fixed, OR returning null is reasonable and the code must always be surrounded with if statements when the output 
from GetResourceLoadTiming() is used.