Fix condition checking for erasing the root

ConflictSet.cpp

@@ -1885,10 +1885,9 @@ void downsize(Node *self, WriteContext *writeContext) {
 // Precondition: self is not the root. May invalidate nodes along the search
 // path to self. May invalidate children of self->parent. Returns a pointer to
 // the node after self. Precondition: `self->entryPresent`
-
 Node *erase(Node *self, WriteContext *writeContext, bool logical) {
   ++writeContext->accum.entries_erased;
-  assert(self->parent != nullptr);
+  assert(self->parent->parent != nullptr);
 
 #if DEBUG_VERBOSE && !defined(NDEBUG)
   fprintf(stderr, "Erase: %s\n", getSearchPathPrintable(self).c_str());