[data.search.aggs] Throw an error when trying to create an agg type that doesn't exist.

src/plugins/data/common/search/aggs/agg_config.test.ts

@@ -680,16 +680,6 @@ describe('AggConfig', () => {
       const json = aggConfig.toExpressionAst()?.arguments.json;
       expect(json).toEqual([JSON.stringify(configStates.params.json)]);
     });
-
-    it(`returns undefined if an expressionName doesn't exist on the agg type`, () => {
-      const ac = new AggConfigs(indexPattern, [], { typesRegistry });
-      const configStates = {
-        type: 'unknown type',
-        params: {},
-      };
-      const aggConfig = ac.createAggConfig(configStates);
-      expect(aggConfig.toExpressionAst()).toBe(undefined);
-    });
   });
 
   describe('#makeLabel', () => {

src/plugins/data/common/search/aggs/agg_configs.test.ts

@@ -150,6 +150,27 @@ describe('AggConfigs', () => {
       );
       expect(ac.aggs).toHaveLength(1);
     });
+
+    it(`throws if trying to add an agg which doesn't have a type in the registry`, () => {
+      const configStates = [
+        {
+          enabled: true,
+          type: 'histogram',
+          params: {},
+        },
+      ];
+
+      const ac = new AggConfigs(indexPattern, configStates, { typesRegistry });
+      expect(() =>
+        ac.createAggConfig({
+          enabled: true,
+          type: 'oops',
+          params: {},
+        })
+      ).toThrowErrorMatchingInlineSnapshot(
+        `"Unable to find a registered agg type for \\"oops\\"."`
+      );
+    });
   });
 
   describe('#getRequestAggs', () => {

src/plugins/data/common/search/aggs/agg_configs.ts

@@ -18,6 +18,7 @@
  */
 
 import _ from 'lodash';
+import { i18n } from '@kbn/i18n';
 import { Assign } from '@kbn/utility-types';
 
 import { ISearchOptions, ISearchSource } from 'src/plugins/data/public';
@@ -122,15 +123,29 @@ export class AggConfigs {
     { addToAggConfigs = true } = {}
   ) => {
     const { type } = params;
-    let aggConfig;
+    const getType = (t: string) => {
+      const typeFromRegistry = this.typesRegistry.get(t);
+
+      if (!typeFromRegistry) {
+        throw new Error(
+          i18n.translate('data.search.aggs.error.aggNotFound', {
+            defaultMessage: 'Unable to find a registered agg type for "{type}".',
+            values: { type: type as string },
+          })
+        );
+      }
 
+      return typeFromRegistry;
+    };
+
+    let aggConfig;
     if (params instanceof AggConfig) {
       aggConfig = params;
       params.parent = this;
     } else {
       aggConfig = new AggConfig(this, {
         ...params,
-        type: typeof type === 'string' ? this.typesRegistry.get(type) : type,
+        type: typeof type === 'string' ? getType(type) : type,
       });
     }