Gauge Panel: fix the default value of thresholds cannot be modified (#20190)

* Panel: fix the default value of thresholds cannot be modified in Gauge panel

* Panel: fix the default value of thresholds cannot be modified in Gauge panel

public/app/features/dashboard/state/PanelModel.test.ts

@@ -24,6 +24,7 @@ describe('PanelModel', () => {
           },
         ],
       },
+      arrayWith2Values: [{ value: 'name' }, { value: 'name2' }],
       showThresholds: true,
     };
 
@@ -43,6 +44,7 @@ describe('PanelModel', () => {
             },
           ],
         },
+        arrayWith2Values: [{ name: 'changed to only one value' }],
       };
 
       modelJson = {
@@ -72,6 +74,10 @@ describe('PanelModel', () => {
       expect(model.getOptions().showThresholds).toBeTruthy();
     });
 
+    it('should apply option defaults but not override if array is changed', () => {
+      expect(model.getOptions().arrayWith2Values.length).toBe(1);
+    });
+
     it('should set model props on instance', () => {
       expect(model.showColumns).toBe(true);
     });

public/app/features/dashboard/state/PanelModel.ts

@@ -255,7 +255,16 @@ export class PanelModel {
     if (plugin.angularConfigCtrl) {
       return;
     }
-    this.options = _.defaultsDeep({}, this.options || {}, plugin.defaults);
+    this.options = _.mergeWith(
+      {},
+      plugin.defaults,
+      this.options || {},
+      (objValue: any, srcValue: any): any => {
+        if (_.isArray(srcValue)) {
+          return srcValue;
+        }
+      }
+    );
   }
 
   pluginLoaded(plugin: PanelPlugin) {