[Resolver] Remove useless check that breaks when tree has no nodes

x-pack/plugins/security_solution/public/resolver/store/data/selectors.test.ts

@@ -14,6 +14,7 @@ import {
   mockTreeWith2AncestorsAndNoChildren,
   mockTreeWith1AncestorAnd2ChildrenAndAllNodesHave2GraphableEvents,
   mockTreeWithAllProcessesTerminated,
+  mockTreeWithNoProcessEvents,
 } from '../mocks/resolver_tree';
 import { uniquePidForProcess } from '../../models/process_event';
 import { EndpointEvent } from '../../../../common/endpoint/types';
@@ -408,4 +409,26 @@ describe('data state', () => {
       expect(selectors.graphableProcesses(state()).length).toBe(4);
     });
   });
+  describe('with a tree with no process events', () => {
+    beforeEach(() => {
+      const tree = mockTreeWithNoProcessEvents();
+      actions.push({
+        type: 'serverReturnedResolverData',
+        payload: {
+          result: tree,
+          // this value doesn't matter
+          databaseDocumentID: '',
+        },
+      });
+    });
+    it('should return an empty layout', () => {
+      expect(selectors.layout(state())).toMatchInlineSnapshot(`
+        Object {
+          "ariaLevels": Map {},
+          "edgeLineSegments": Array [],
+          "processNodePositions": Map {},
+        }
+      `);
+    });
+  });
 });

x-pack/plugins/security_solution/public/resolver/store/data/selectors.ts

@@ -374,9 +374,9 @@ export const layout = createSelector(
     // find the origin node
     const originNode = indexedProcessTreeModel.processEvent(indexedProcessTree, originID);
 
-    if (!originNode) {
-      // this should only happen if the `ResolverTree` from the server has an entity ID with no matching lifecycle events.
-      throw new Error('Origin node not found in ResolverTree');
+    if (originNode === null) {
+      // If a tree is returned that has no process events for the origin, this can happen.
+      return taxiLayout;
     }
 
     // Find the position of the origin, we'll center the map on it intrinsically

x-pack/plugins/security_solution/public/resolver/store/mocks/resolver_tree.ts

@@ -226,3 +226,33 @@ export function mockTreeWith1AncestorAnd2ChildrenAndAllNodesHave2GraphableEvents
     lifecycle: [origin, originClone],
   } as unknown) as ResolverTree;
 }
+
+export function mockTreeWithNoProcessEvents(): ResolverTree {
+  return {
+    entityID: 'entityID',
+    children: {
+      childNodes: [],
+      nextChild: null,
+    },
+    relatedEvents: {
+      events: [],
+      nextEvent: null,
+    },
+    relatedAlerts: {
+      alerts: [],
+      nextAlert: null,
+    },
+    lifecycle: [],
+    ancestry: {
+      ancestors: [],
+      nextAncestor: null,
+    },
+    stats: {
+      totalAlerts: 0,
+      events: {
+        total: 0,
+        byCategory: {},
+      },
+    },
+  };
+}