Implemented PR suggestions - is instead of equality operator

Co-authored-by: Nikolaj Geisle <70372949+Zeegaan@users.noreply.github.com>

src/Umbraco.Infrastructure/Services/Implement/CacheInstructionService.cs

@@ -247,7 +247,7 @@ namespace Umbraco.Cms.Core.Services.Implement
         /// </summary>
         private bool TryDeserializeInstructions(CacheInstruction instruction, out JArray jsonInstructions)
         {
-            if (instruction.Instructions == null)
+            if (instruction.Instructions is null)
             {
                 _logger.LogError("Failed to deserialize instructions ({DtoId}: 'null').", instruction.Id);
                 jsonInstructions = null;