Steps to reproduce:

1. Install a signed tarball package
2. Click on "Locate" to find the package.json file or find it in the Project Browser
3. Click on the package.json file to select it in the Inspector
4. Observe the console

Actual results: Infinite NullReferenceException in the console
{code:java}
NullReferenceException: Object reference not set to an instance of an object
UnityEditor.PackageManager.UI.Internal.PackageManifestImporterEditor.OnInspectorGUI () (at <67e86cf8daae4a16b6d0ff7c1d13515c>:0)
UnityEditor.UIElements.InspectorElement+<>c__DisplayClass83_0.<CreateInspectorElementUsingIMGUI>b__1 () (at <67e86cf8daae4a16b6d0ff7c1d13515c>:0)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&) {code}
Expected results: Package.json is shown in the inspector with no errors in the console

Reproducible with versions: 6000.3.0a3, 6000.4.0a2

Not reproducible with versions: 6000.3.0a2

Tested on (OS): macOS

Notes:

• With 6000.3.0a2 there's no locate button available in PM, so the file has to be located manually