Don't throw error if only a segmentation layer exists (#4265)

* don't throw error if only a segmentation layer exists
* update changelog
* Merge branch 'master' into optional-color-layer

CHANGELOG.md

@@ -48,6 +48,7 @@ For upgrade instructions, please check the [migration guide](MIGRATIONS.md).
 - Fixed the error messages when trying to access a dataset with insufficient permissions. [#4244](https://github.com/scalableminds/webknossos/pull/4244)
 - Fixed the upload of volume tracings by recognizing the correct format of the fallback layer. [#4248](https://github.com/scalableminds/webknossos/pull/4248)
 - Fixed an imprecision when exporting an NML via the front-end. [#4262](https://github.com/scalableminds/webknossos/pull/4262)
+- Fixed viewing and tracing of datasets which only contain a segmentation layer. [#4265](https://github.com/scalableminds/webknossos/pull/4265)
 
 ### Removed
 -

frontend/javascripts/oxalis/model_initialization.js

@@ -378,7 +378,7 @@ function initializeDataLayerInstances(
     window.mappings = setupGlobalMappingsObject(dataLayers[segmentationLayer.name]);
   }
 
-  if (getColorLayers(dataset).length === 0) {
+  if (getColorLayers(dataset).length === 0 && segmentationLayer == null) {
     Toast.error(messages["dataset.no_data"]);
     throw HANDLED_ERROR;
   }