[Lens] Fix crash in transition from unique count to last value

x-pack/plugins/lens/public/indexpattern_datasource/operations/layer_helpers.test.ts

@@ -2175,7 +2175,7 @@ describe('state_helpers', () => {
       expect(errors).toHaveLength(1);
     });
 
-    it('should consider incompleteColumns before layer columns', () => {
+    it('should ignore incompleteColumns when checking for errors', () => {
       const savedRef = jest.fn().mockReturnValue(['error 1']);
       const incompleteRef = jest.fn();
       operationDefinitionMap.testReference.getErrorMessage = savedRef;
@@ -2197,9 +2197,9 @@ describe('state_helpers', () => {
           col1: { operationType: 'testIncompleteReference' },
         },
       });
-      expect(savedRef).not.toHaveBeenCalled();
-      expect(incompleteRef).toHaveBeenCalled();
-      expect(errors).toBeUndefined();
+      expect(savedRef).toHaveBeenCalled();
+      expect(incompleteRef).not.toHaveBeenCalled();
+      expect(errors).toHaveLength(1);
 
       delete operationDefinitionMap.testIncompleteReference;
     });

x-pack/plugins/lens/public/indexpattern_datasource/operations/layer_helpers.ts

@@ -867,11 +867,7 @@ export function updateLayerIndexPattern(
 export function getErrorMessages(layer: IndexPatternLayer): string[] | undefined {
   const errors: string[] = [];
   Object.entries(layer.columns).forEach(([columnId, column]) => {
-    // If we're transitioning to another operation, check for "new" incompleteColumns rather
-    // than "old" saved operation on the layer
-    const columnFinalRef =
-      layer.incompleteColumns?.[columnId]?.operationType || column.operationType;
-    const def = operationDefinitionMap[columnFinalRef];
+    const def = operationDefinitionMap[column.operationType];
     if (def.getErrorMessage) {
       errors.push(...(def.getErrorMessage(layer, columnId) ?? []));
     }

x-pack/test/functional/apps/lens/smokescreen.ts

@@ -514,6 +514,28 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
       );
     });
 
+    it('should transition from unique count to last value', async () => {
+      await PageObjects.visualize.navigateToNewVisualization();
+      await PageObjects.visualize.clickVisType('lens');
+      await PageObjects.lens.goToTimeRange();
+
+      await PageObjects.lens.configureDimension({
+        dimension: 'lnsXY_yDimensionPanel > lns-empty-dimension',
+        operation: 'cardinality',
+        field: 'ip',
+      });
+      await PageObjects.lens.configureDimension({
+        dimension: 'lnsXY_yDimensionPanel > lns-dimensionTrigger',
+        operation: 'last_value',
+        field: 'bytes',
+        isPreviousIncompatible: true,
+      });
+
+      expect(await PageObjects.lens.getDimensionTriggerText('lnsXY_yDimensionPanel')).to.eql(
+        'Last value of bytes'
+      );
+    });
+
     it('should allow to change index pattern', async () => {
       await PageObjects.lens.switchFirstLayerIndexPattern('log*');
       expect(await PageObjects.lens.getFirstLayerIndexPattern()).to.equal('log*');