B #-: Fix default labels parsing

(cherry picked from commit 51cda83)

Author: rsmontero

src/onedb/local/6.10.0_to_7.0.0.rb

@@ -112,7 +112,8 @@ def feature_6648
                                    YAML.load_file(sunstone_default_labels)
                                        &.dig('labels_groups')
                                        &.transform_values do |labels|
-                                         labels.map { |label| "$#{sanitize_label(label.strip)}" }
+                                           next unless labels
+                                           [labels].flatten.map { |label| "$#{sanitize_label(label&.strip)}" }
                                        end
                                  else
                                    {}