Dereference null return value

If the function actually returns a null value, a null pointer dereference will occur. Return value of function which returns null is dereferenced without checking
/data/mci/9292c3def3822c0dfd66af88847bcc64/bazel_cache/004acac643584f695e6309f72694e5ad/execroot/_main/src/mongo/db/startup_recovery.cpp:636: NULL_RETURNS 143624 Assigning: "collection" = "nullptr" return value from "lookupCollectionByNamespace".