Add nil checks for manager_uuids and references

Add nil checks for manager_uuids and references, nil references
lead to non existent elements, so we don't want them stored.

app/models/manager_refresh/inventory_collection.rb

@@ -1009,7 +1009,7 @@ def find_in_db(manager_uuid)
       else
         return db_data_index[manager_uuid] if db_data_index && db_data_index[manager_uuid]
         # We haven't found the reference, lets add it to the list of references and load it
-        references << manager_uuid unless references.include?(manager_uuid) # O(1) since references is Set
+        references << manager_uuid if manager_uuid
       end
 
       # Put our existing data keys into loaded references
@@ -1081,6 +1081,7 @@ def extract_references(new_references = [])
       hash_uuids_by_ref = []
 
       new_references.each do |manager_uuid|
+        next if manager_uuid.nil?
         uuids = manager_uuid.split(stringify_joiner)
 
         reference = {}

app/models/manager_refresh/inventory_collection/scanner.rb

@@ -61,7 +61,8 @@ def scan!
 
           if targeted? && parent_inventory_collections.blank?
             # We want to track what manager_uuids we should query from a db, for the targeted refresh
-            manager_uuids << inventory_object.manager_uuid
+            manager_uuid = inventory_object.manager_uuid
+            manager_uuids << manager_uuid if manager_uuid
           end
         end
 
@@ -116,14 +117,17 @@ def scan_inventory_object_attribute!(key, value)
             # TODO(lsmola) solve the :key, since that requires data from the actual reference. At best our DB should be
             # designed the way, we don't duplicate the data, but rather get them with a join. (3NF!)
 
-            value_inventory_collection.find_or_build(value.ems_ref)
-            value_inventory_collection.skeletal_manager_uuids << value.ems_ref
+            if value.ems_ref
+              value_inventory_collection.find_or_build(value.ems_ref)
+              value_inventory_collection.skeletal_manager_uuids << value.ems_ref
+            end
           end
         end
 
         # Storing a reference in the target inventory_collection, then each IC knows about all the references and can
         # e.g. load all the referenced uuids from a DB
-        value_inventory_collection.references << value.to_s
+        value_to_s = value.to_s
+        value_inventory_collection.references << value_to_s if value_to_s
 
         if inventory_object_lazy?(value)
           # Storing if attribute is a transitive dependency, so a lazy_find :key results in dependency