Reproduction steps:
1. Create a new project or open an existing one
2. Install Device Simulator package
3. Install Input System package
4. Open Device Simulator window (Window -> General -> Device Simulator)

Expected result: Device Simulator window is not empty and no errors are thrown
Actual result: Device Simulator window is empty and NullReferenceException error is thrown

Reproduces on: 2020.2.0b3 (2.2.3-preview), 2020.2.0b9 (2.2.3-preview), 2021.1.0a1 (2.2.3-preview), 2021.1.0a2 (2.2.3-preview)

Does not reproduce on: 2020.1.11f1 (2.2.3-preview), 2020.2.0b2 (2.2.3-preview)

Error message:
NullReferenceException: Object reference not set to an instance of an object
Unity.DeviceSimulator.InputProvider..ctor () (at Library/PackageCache/com.unity.device-simulator@2.2.3-preview/Editor/Input/InputProvider.cs:46)
Unity.DeviceSimulator.SimulatorWindow.OnEnable () (at Library/PackageCache/com.unity.device-simulator@2.2.3-preview/Editor/SimulatorWindow.cs:84)
UnityEditorInternal.InternalEditorUtility:LoadSerializedFileAndForget(String)
UnityEditor.WindowLayout:LoadDefaultWindowPreferences()

Notes:
Different Input System and Device Simulator package version combinations do not fix the issue.