Reproduction steps:
1. Open attached project "1292029"
2. Go to Window > Analysis > Memory Profiler
3. Dock the opened Memory Profiler window next to the Game window and press "Capture Editor" to create a memory snapshot
4. Enter and exit Play Mode
5. Create a new script to trigger a recompile

Expected result: No errors are thrown in the Console window
Actual result: NullReferenceException is thrown

Reproducible with: 2018.4.30f1, 2019.4.16f1, 2020.1.16f1, 2020.2.0b14, 2021.1.0a8

Reproducible with package versions: 0.2.4-preview.1, 0.2.6-preview.1
Could not test with package versions: 0.2.3-preview.2 (errors)

Note: The error doesn't seem to be reproducible when the Memory Profiler window is undocked or when it is docked and visible in the editor.

Full error:
NullReferenceException: Object reference not set to an instance of an object
Unity.MemoryProfiler.Editor.MemoryProfilerWindow.OnDisable () (at Library/PackageCache/com.unity.memoryprofiler@0.2.6-preview.1/Editor/MemoryProfilerWindow.cs:684)