diff --git a/src/Altinn.App.Api/Altinn.App.Api.csproj b/src/Altinn.App.Api/Altinn.App.Api.csproj
index bb16215f2..3bb643875 100644
--- a/src/Altinn.App.Api/Altinn.App.Api.csproj
+++ b/src/Altinn.App.Api/Altinn.App.Api.csproj
@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk.Web">
+<Project Sdk="Microsoft.NET.Sdk.Web">
 
   <PropertyGroup>
     <TargetFrameworks>net6.0</TargetFrameworks>
@@ -13,7 +13,7 @@
     <RepositoryType>git</RepositoryType>
     <RepositoryUrl>https://github.com/Altinn/app-lib-dotnet</RepositoryUrl>
     <IsPackable>true</IsPackable>
-    <ImplicitUsings>true</ImplicitUsings>
+    <ImplicitUsings>enable</ImplicitUsings>
 
     <!-- SonarCloud requires a ProjectGuid to separate projects. -->
     <ProjectGuid>{E8F29FE8-6B62-41F1-A08C-2A318DD08BB4}</ProjectGuid>
diff --git a/src/Altinn.App.Api/Controllers/PagesController.cs b/src/Altinn.App.Api/Controllers/PagesController.cs
index c9181ad4e..dc212350a 100644
--- a/src/Altinn.App.Api/Controllers/PagesController.cs
+++ b/src/Altinn.App.Api/Controllers/PagesController.cs
@@ -31,8 +31,8 @@ public class PagesController : ControllerBase
         /// <param name="pageOrder">The page order service</param>
         public PagesController(
             IAppModel appModel,
-            IAppResources resources, 
-            IPageOrder pageOrder, 
+            IAppResources resources,
+            IPageOrder pageOrder,
             ILogger<PagesController> logger)
         {
             _appModel = appModel;
diff --git a/src/Altinn.App.Api/Helpers/StartupHelper.cs b/src/Altinn.App.Api/Helpers/StartupHelper.cs
index 9bac3be5f..6ef8a00ea 100644
--- a/src/Altinn.App.Api/Helpers/StartupHelper.cs
+++ b/src/Altinn.App.Api/Helpers/StartupHelper.cs
@@ -43,6 +43,6 @@ public static string GetApplicationId()
     {
         string appMetaDataString = File.ReadAllText("config/applicationmetadata.json");
         JObject appMetadataJObject = JObject.Parse(appMetaDataString);
-        return appMetadataJObject.SelectToken("id").Value<string>();
+        return appMetadataJObject.SelectToken("id")?.Value<string>() ?? throw new Exception("config/applicationmetadata.json does not contain an \"id\" property");
     }
 }
\ No newline at end of file
diff --git a/test/Altinn.App.Api.Tests/Controllers/ValidateControllerValidateDataTests.cs b/test/Altinn.App.Api.Tests/Controllers/ValidateControllerValidateDataTests.cs
index 3cb418a19..2e76cc67c 100644
--- a/test/Altinn.App.Api.Tests/Controllers/ValidateControllerValidateDataTests.cs
+++ b/test/Altinn.App.Api.Tests/Controllers/ValidateControllerValidateDataTests.cs
@@ -9,6 +9,7 @@
 using Altinn.App.Core.Models.Validation;
 using Altinn.Platform.Storage.Interface.Models;
 using Microsoft.AspNetCore.Mvc;
+using FluentAssertions;
 using Moq;
 using Xunit;
 
@@ -221,7 +222,7 @@ public async Task TestValidateData(ValidateDataTestScenario testScenario)
         {
             var result = await validateController.ValidateData(org, app, instanceOwnerId, testScenario.InstanceId,
                 testScenario.DataGuid);
-            Assert.IsType(testScenario.ExpectedResult, result);
+            result.Should().BeOfType(testScenario.ExpectedResult);
         }
         else
         {
diff --git a/test/Altinn.App.Api.Tests/Mocks/Authentication/JwtCookiePostConfigureOptionsStub.cs b/test/Altinn.App.Api.Tests/Mocks/Authentication/JwtCookiePostConfigureOptionsStub.cs
index 6ff3aae21..2e3a9f2ce 100644
--- a/test/Altinn.App.Api.Tests/Mocks/Authentication/JwtCookiePostConfigureOptionsStub.cs
+++ b/test/Altinn.App.Api.Tests/Mocks/Authentication/JwtCookiePostConfigureOptionsStub.cs
@@ -14,7 +14,7 @@ namespace Altinn.App.Api.Tests.Mocks.Authentication
     public class JwtCookiePostConfigureOptionsStub : IPostConfigureOptions<JwtCookieOptions>
     {
         /// <inheritdoc />
-        public void PostConfigure(string name, JwtCookieOptions options)
+        public void PostConfigure(string? name, JwtCookieOptions options)
         {
             if (string.IsNullOrEmpty(options.JwtCookieName))
             {
diff --git a/test/Altinn.App.Api.Tests/Mocks/PepWithPDPAuthorizationMockSI.cs b/test/Altinn.App.Api.Tests/Mocks/PepWithPDPAuthorizationMockSI.cs
index a4ad04ad2..bb0100c59 100644
--- a/test/Altinn.App.Api.Tests/Mocks/PepWithPDPAuthorizationMockSI.cs
+++ b/test/Altinn.App.Api.Tests/Mocks/PepWithPDPAuthorizationMockSI.cs
@@ -61,7 +61,7 @@ public async Task<XacmlJsonResponse> GetDecisionForRequest(XacmlJsonRequestRoot
             }
             catch
             {
-                return null;
+                return null!;
             }
         }