Fix spawner_ui_config.yaml to use correct null values for configurations

Previously, any empty configuration for the images, affinity configurations, tolerations, and gpu configurations fields were output as nulls in the yaml (eg: "value:").  The jupyter web app does not handle null values for some of these fields, instead requiring empty strings or empty lists.  This commit updates the template to ensure we always output the correct empty values.

charms/jupyter-ui/src/templates/spawner_ui_config.yaml.j2

@@ -38,12 +38,18 @@ spawnerFormDefaults:
   ################################################################
   image:
     # the default container image
+    {%- if jupyter_images_default %}
     value: {{ jupyter_images_default }}
+    {%- else %}
+    value: ""
+    {%- endif %}
 
     # the list of available container images in the dropdown
-    options:
     {%- if jupyter_images | length > 0 %}
+    options:
     {{ jupyter_images | to_yaml | indent(4) }}
+    {%- else %}
+    options: []
     {%- endif %}
 
   ################################################################
@@ -59,12 +65,18 @@ spawnerFormDefaults:
   ################################################################
   imageGroupOne:
     # the default container image
+    {%- if vscode_images_default %}
     value: {{ vscode_images_default }}
+    {%- else %}
+    value: ""
+    {%- endif %}
 
     # the list of available container images in the dropdown
-    options:
     {%- if vscode_images | length > 0 %}
+    options:
     {{ vscode_images | to_yaml | indent(4) }}
+    {%- else %}
+    options: []
     {%- endif %}
 
   ################################################################
@@ -82,12 +94,18 @@ spawnerFormDefaults:
   ################################################################
   imageGroupTwo:
     # the default container image
+    {%- if rstudio_images_default %}
     value: {{ rstudio_images_default }}
+    {%- else %}
+    value: ""
+    {%- endif %}
 
     # the list of available container images in the dropdown
-    options:
     {%- if rstudio_images | length > 0 %}
+    options:
     {{ rstudio_images | to_yaml | indent(4) }}
+    {%- else %}
+    options: []
     {%- endif %}
 
   ################################################################
@@ -127,14 +145,20 @@ spawnerFormDefaults:
     value:
       # the `limitKey` of the default vendor
       # (to have no default, set as "")
+      {%- if gpu_vendors_default %}
       vendor: {{ gpu_vendors_default }}
+      {%- else %}
+      vendor: ""
+      {%- endif %}
 
       # the list of available vendors in the dropdown
       #  `limitsKey` - what will be set as the actual limit
       #  `uiName` - what will be displayed in the dropdown UI
-      vendors:
       {%- if gpu_vendors | length > 0 %}
+      vendors:
       {{ gpu_vendors | to_yaml | indent(6) }}
+      {%- else %}
+      vendors: []
       {%- endif %}
 
       # the default value of the limit
@@ -200,12 +224,18 @@ spawnerFormDefaults:
     # the `configKey` of the default affinity config
     # (to have no default, set as "")
     # (if `readOnly`, the default `value` will be the only accessible option)
+    {%- if affinity_options_default %}
     value: {{ affinity_options_default }}
+    {%- else %}
+    value: ""
+    {%- endif %}
 
     # the list of available affinity configs in the dropdown
-    options:
     {%- if affinity_options | length > 0 %}
+    options:
     {{ affinity_options | to_yaml | indent(4) }}
+    {%- else %}
+    options: []
     {%- endif %}
 
     #options:
@@ -243,12 +273,18 @@ spawnerFormDefaults:
     # the `groupKey` of the default toleration group
     # (to have no default, set as "")
     # (if `readOnly`, the default `value` will be the only accessible option)
+    {%- if tolerations_options_default %}
     value: {{ tolerations_options_default }}
+    {%- else %}
+    value: ""
+    {%- endif %}
 
     # the list of available toleration groups in the dropdown
-    options:
     {%- if tolerations_options | length > 0 %}
+    options:
     {{ tolerations_options | to_yaml | indent(4) }}
+    {%- else %}
+    options: []
     {%- endif %}
 
     #options:
@@ -301,9 +337,11 @@ spawnerFormDefaults:
 
     # the list of PodDefault names that are selected by default
     # (take care to ensure these PodDefaults exist in Profile Namespaces)
-    value:
     {%- if default_poddefaults | length > 0 %}
+    value:
     {{ default_poddefaults | to_yaml | indent(4) }}
+    {%- else %}
+    value: []
     {%- endif %}
 
   ################################################################

charms/jupyter-ui/tests/unit/test_operator.py

@@ -3,7 +3,7 @@
 #
 
 """Unit tests for JupyterUI Charm."""
-
+import copy
 import logging
 from contextlib import nullcontext as does_not_raise
 from unittest.mock import MagicMock, patch
@@ -428,19 +428,8 @@ def test_render_jwa_file(
         # Arrange
         render_args = render_jwa_file_with_images_config_args
 
-        # Build the expected results, converting empty values to None to match the output of the
-        # function
-        expected = {
-            k: (
-                OptionsWithDefault(
-                    default=(config.default if config.default else None),
-                    options=(config.options if config.options else None),
-                )
-                if k != "gpu_number_default"
-                else config
-            )
-            for k, config in render_args.items()
-        }
+        # Build the expected results
+        expected = copy.deepcopy(render_args)
 
         harness.set_leader(True)
         harness.begin()