Add guard class.

.github/workflows/dotnet.yml

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+# This workflow will build a .NET project
+# For more information see: https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-net
+
+name: .NET
+
+on:
+  push:
+    branches: [ "main", "develop" ]
+  pull_request:
+    branches: [ "main", "develop" ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          filter: tree:0
+
+      - name: Get tags
+        run: git fetch --tags origin
+
+      - name: Setup .NET
+        uses: actions/setup-dotnet@v4
+        with:
+          dotnet-version: 8.0.x
+
+      - name: Restore dependencies
+        run: dotnet restore
+
+      - name: Build
+        run: dotnet build --configuration Release --no-restore
+
+      - name: Test
+        run: dotnet test --configuration Release -p:CollectCoverage=true
+
+      - name: Publish Nuget
+        run: |
+          dotnet nuget push '**/*.nupkg' -k ${NUGET} -s https://api.nuget.org/v3/index.json --skip-duplicate --no-symbols
+        env:
+          NUGET: ${{ secrets.NUGET }}

.gitignore

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+.vs
+bin
+obj

Utility.Guard.sln

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+Microsoft Visual Studio Solution File, Format Version 12.00
+# 17
+VisualStudioVersion = 17.10.35027.167
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Utility.Guard", "Utility.Guard\Utility.Guard.csproj", "{1DF6CF00-3907-40A3-BA69-B32788F37F4C}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{1DF6CF00-3907-40A3-BA69-B32788F37F4C}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{1DF6CF00-3907-40A3-BA69-B32788F37F4C}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{1DF6CF00-3907-40A3-BA69-B32788F37F4C}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{1DF6CF00-3907-40A3-BA69-B32788F37F4C}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {7D25D4C6-E7A0-4490-8BDE-9076CA666008}
+	EndGlobalSection
+EndGlobal

Utility.Guard/Guard.cs

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+using System.Linq.Expressions;
+
+namespace Utility;
+
+public static class Guard
+{
+    public static T ThrowIfNull<T>(T item)
+    {
+        if (item is null)
+        {
+            throw new InvalidOperationException();
+        }
+
+        return item;
+    }
+
+    public static T ThrowIfNotNull<T>(T item)
+    {
+        if (item is not null)
+        {
+            throw new InvalidOperationException();
+        }
+
+        return item;
+    }
+
+    public static int ThrowIfIntegerNotInRange(int item, int start, int end)
+    {
+        if (item >= start && item <= end)
+        {
+            throw new InvalidOperationException();
+        }
+
+        return item;
+    }
+
+    public static string ThrowIfStringNullOrEmpty(string value)
+    {
+        if (string.IsNullOrEmpty(value))
+        {
+            throw new InvalidOperationException();
+        }
+
+        return value;
+    }
+}

Utility.Guard/Utility.Guard.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+	<PropertyGroup>
+		<TargetFramework>netstandard20</TargetFramework>
+		<ImplicitUsings>enable</ImplicitUsings>
+		<Nullable>enable</Nullable>
+		<GeneratePackageOnBuild>True</GeneratePackageOnBuild>
+		<Authors>Simon Jefferies</Authors>
+		<Company>Simon Jefferies</Company>
+		<Description></Description>
+		<PackageLicenseExpression>MIT</PackageLicenseExpression>
+		<LangVersion>latest</LangVersion>
+	</PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="MinVer" Version="*">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+  </ItemGroup>
+
+</Project>