fix return value in networkelementServiceMock, nolint in pluginServiceMock

controller/nucleus/networkElementServiceMock.go

 package nucleus
 
 import (
+	"code.fbi.h-da.de/danet/gosdn/controller/customerrs"
 	"code.fbi.h-da.de/danet/gosdn/controller/interfaces/networkelement"
 	"code.fbi.h-da.de/danet/gosdn/controller/store"
 	"github.com/google/uuid"
@@ -66,12 +67,12 @@ func (t *NetworkElementServiceMock) Get(query store.Query) (networkelement.Netwo
 		// Second search for name
 		id, ok := t.nameLookupTable[query.Name]
 		if !ok {
-			return nil, nil
+			return nil, customerrs.CouldNotFindError{Name: query.Name}
 		}
 
 		item, ok := t.Store[id]
 		if !ok {
-			return nil, nil
+			return nil, customerrs.CouldNotFindError{ID: id}
 		}
 
 		return item, nil

controller/nucleus/pluginServiceMock.go

@@ -62,5 +62,5 @@ func (t *PluginServiceMock) GetAll() ([]plugin.Plugin, error) {
 // RequestPlugin is a mock for requesting a plugin from the registry.
 // TODO: add plugin mock here.
 func (t *PluginServiceMock) RequestPlugin(uuid.UUID) (plugin.Plugin, error) {
-	return nil, nil
+	return nil, nil //nolint:nilnil
 }