How to reproduce:
1. Open the attached package on HDRP project
2. Open SG
3. Connect Vector3 node to Position block
4. Save ShaderGraph

Expected result: VFX is displayed at 0,0,0 pos
Actual result: VFX disappears and error is thrown to the console

Reproducible with: 2021.2, 2022.2(public 12.0.0, master)

Note: Happens with any kind of vector when assigning to blocks - Position, Smoothness, Metallic, etc.

Error message:
ArgumentNullException: Value cannot be null.
Parameter name: key
System.Collections.Generic.Dictionary`2[TKey,TValue].FindEntry (TKey key) (at <231f6c5a042647adb84a9cc42c982c35>:0)
System.Collections.Generic.Dictionary`2[TKey,TValue].ContainsKey (TKey key) (at <231f6c5a042647adb84a9cc42c982c35>:0)
UnityEditor.VFX.VFXCodeGenerator.BuildFragInputsGeneration (UnityEditor.VFX.VFXContext context, UnityEditor.VFX.VFXContextCompiledData contextData, System.Boolean useFragInputs, System.String& buildFragInputsGeneration) (at C:/Users/vita.skruibyte/Documents/SRP/com.unity.visualeffectgraph/Editor/Compiler/VFXCodeGenerator.cs:483)