[bugfix] Check that oldData is defined before trying to migrate (#7537)

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## Summary
<!-- Describe your changes here, include the motivation/context, test coverage, -->
<!-- the type of change i.e. breaking change, new feature, or bug fix -->
<!-- and related GitHub issue or screenshots (if applicable). -->


FIxes issue where launchpad config gets wiped out whenever you load the launchpad.

## Test Plan
<!--- Please describe the tests you have added and your testing environment (if applicable). -->
 
Made a change to launchpad config. Reload the page. See that the launchpad config sticks around.



## Checklist
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- [ ] My change requires a change to the documentation and I have updated the documentation accordingly.
- [ ] I have added tests to cover my changes.

js_modules/dagit/packages/core/src/app/ExecutionSessionStorage.tsx

@@ -176,9 +176,9 @@ export function useExecutionSessionStorage(
 
   // TODO: Remove this migration logic in a few patches when we know the old namespace is likely no longer being used
   const oldDataMigrated = React.useRef(false);
-  if (!oldDataMigrated.current) {
+  if (oldData && !oldDataMigrated.current) {
     onSave(oldData);
-    window.localStorage.removeItem(oldNamespace);
+    window.localStorage.removeItem(getKey(oldNamespace));
     oldDataMigrated.current = true;
   }
 

js_modules/dagit/packages/core/src/app/__tests__/ExecutionSessionStorage.test.tsx

@@ -0,0 +1,89 @@
+import {render} from '@testing-library/react';
+import * as React from 'react';
+
+import {TestProvider} from '../../testing/TestProvider';
+import {AppContext} from '../AppContext';
+import {useExecutionSessionStorage} from '../ExecutionSessionStorage';
+
+function mockedLocalStorage() {
+  let store = {};
+  return {
+    setItem(key: string, item: any) {
+      store[key] = item;
+    },
+    getItem(key: string) {
+      return store[key];
+    },
+    removeItem(key: string) {
+      delete store[key];
+    },
+    clear() {
+      store = {};
+    },
+    get length() {
+      return Object.keys(store).length;
+    },
+    key(n: number) {
+      return Object.keys(store)[n];
+    },
+  };
+}
+
+let BASE_PATH = '';
+const REPO_ADDRESS = {
+  name: 'test-name',
+  location: 'test-location',
+};
+
+const PIPELINE = 'test-pipeline';
+
+const oldKeyFormat = (repoAddress: typeof REPO_ADDRESS, pipelineOrJobName: string) => {
+  return `dagit.v2.${repoAddress.name}.${pipelineOrJobName}`;
+};
+
+const newKeyFormat = (
+  basePath: string,
+  repoAddress: typeof REPO_ADDRESS,
+  pipelineOrJobName: string,
+) => {
+  return `dagit.v2.${basePath}-${repoAddress.location}-${repoAddress.name}-${pipelineOrJobName}`;
+};
+
+describe('ExecutionSessionStorage', () => {
+  const originalLocalStorage = window.localStorage;
+  beforeEach(() => {
+    window.localStorage = mockedLocalStorage();
+    jest.resetModules();
+  });
+  afterEach(() => {
+    window.localStorage = originalLocalStorage;
+  });
+
+  it('Migrates old localStorage data from old format', () => {
+    const testData = {sessions: {test: 'test'}, current: 'test'};
+    const oldFormat = oldKeyFormat(REPO_ADDRESS, PIPELINE);
+    const newFormat = newKeyFormat(BASE_PATH, REPO_ADDRESS, PIPELINE);
+
+    window.localStorage.setItem(oldFormat, JSON.stringify(testData));
+
+    function TestComponent() {
+      const context = React.useContext(AppContext);
+      BASE_PATH = context.basePath;
+      const [data] = useExecutionSessionStorage(REPO_ADDRESS, PIPELINE);
+      expect(data).toEqual(testData);
+      return <div />;
+    }
+
+    render(
+      <TestProvider>
+        <TestComponent />
+      </TestProvider>,
+    );
+
+    // Its at the new key
+    expect(JSON.parse(window.localStorage.getItem(newFormat) as any)).toEqual(testData);
+
+    // old key is deleted
+    expect(window.localStorage.getItem(oldFormat)).toEqual(null);
+  });
+});