Reproduction steps:
1. Create a new project
2. Install "Shader Graph" package
3. Import "BrokenMat.mat" asset

Expected result: Only "File is either empty or corrupted, please verify the file contents." error appears in the Console
Actual result: NullReferenceException and "File is either empty or corrupted, please verify the file contents." errors appear in the Console

Reproducible with: 7.7.1 (2019.4.37f1), 10.8.1 (2020.3.31f1), 12.1.6 (2021.2.16f1), 13.1.7 (2022.1.0b12), 14.0.1 (2022.2.0a8)

Notes:
- To make this error appear in 2019.4 and 2020.3 streams either URP or HDRP must be also installed

Full errors:
Error loading the file 'Assets/BrokenMat.mat'. File is either empty or corrupted, please verify the file contents.
UnityEngine.GUIUtility:ProcessEvent (int,intptr,bool&)

NullReferenceException: Object reference not set to an instance of an object
UnityEditor.Rendering.BuiltIn.MaterialPostprocessor.OnPostprocessAllAssets (System.String\[] importedAssets, System.String\[] deletedAssets, System.String\[] movedAssets, System.String\[] movedFromAssetPaths) (at Library/PackageCache/com.unity.shadergraph@14.0.1/Editor/Generation/Targets/BuiltIn/Editor/AssetPostProcessors/MaterialPostprocessor.cs:77)
System.Reflection.RuntimeMethodInfo.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object\[] parameters, System.Globalization.CultureInfo culture) (at <86bc6b6562c6434a9e767382eb38f2c1>:0)
Rethrow as TargetInvocationException: Exception has been thrown by the target of an invocation.
System.Reflection.RuntimeMethodInfo.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object\[] parameters, System.Globalization.CultureInfo culture) (at <86bc6b6562c6434a9e767382eb38f2c1>:0)
System.Reflection.MethodBase.Invoke (System.Object obj, System.Object\[] parameters) (at <86bc6b6562c6434a9e767382eb38f2c1>:0)
UnityEditor.AssetPostprocessingInternal.InvokeMethod (System.Reflection.MethodInfo method, System.Object\[] args) (at /Users/bokken/buildslave/unity/build/Editor/Mono/AssetPostprocessor.cs:1145)
UnityEditor.AssetPostprocessingInternal.PostprocessAllAssets (System.String\[] importedAssets, System.String\[] addedAssets, System.String\[] deletedAssets, System.String\[] movedAssets, System.String\[] movedFromPathAssets, System.Boolean didDomainReload) (at /Users/bokken/buildslave/unity/build/Editor/Mono/AssetPostprocessor.cs:385)