A utility class to validate parameters (add to your projects as a linked file)

Guard.cs

using System;
using System.Collections ;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis ;
using System.Linq ;
using JetBrains.Annotations ;

// PLEASE DON'T MAKE ANYTHING PUBLIC IN THIS FILE.  THIS FILE (AND JETBRAINS.ANNOTATIONS) IS INTENDED
// TO BE INCLUDED AS A LINKED FILE INTO WHATEVER PROJECTS NEEDS THEM.  

internal class CoverageExcludeAttribute : Attribute
{
}

/// <summary>
/// Guard class, used for guard clauses and argument validation.
/// <para>
/// Don't put this in a namespace or an assembly, simply add it your project as a linked file.  
/// This is to stop ambiguous instances where 2 or more assemblies contains this type.
/// </para>
/// </summary>
[CoverageExclude]
[DebuggerNonUserCode] // (see http://blog.functionalfun.net/2008/05/debuggernonusercode-suppressing.html)
static class Guard
{
	[DebuggerHidden]
	[AssertionMethod]
    [PublicAPI]
	public static void ArgumentNotNull< T >(
		[NotNull, InvokerParameterName] string argName,
		[AssertionCondition( AssertionConditionType.IS_NOT_NULL ), NoEnumeration] T argValue ) where T : class
	{
		if( argValue == null )
		{
			throw new ArgumentNullException( argName ) ;
		}
	}

	[DebuggerHidden]
	[SuppressMessage(
		"Microsoft.Usage",
		"CA2208:InstantiateArgumentExceptionsCorrectly",
		Justification = @"Cannot call the overload that takes a parameter name as I'm not passed a parameter name." )]
	[AssertionMethod]
    [PublicAPI]
	public static void ArgumentNotNull< T >(
		[AssertionCondition( AssertionConditionType.IS_NOT_NULL ), NoEnumeration] T value ) where T : class
	{
		if( value == null )
		{
			throw new ArgumentNullException( ) ;
		}
	}

	[DebuggerHidden]
	[AssertionMethod]
    [PublicAPI]
	public static void GenericArgumentNotNull<T>(
		[NotNull, InvokerParameterName] string argName,
		[AssertionCondition(AssertionConditionType.IS_NOT_NULL), NoEnumeration] T arg)
	{
		Type type = typeof(T);

		if (!type.IsValueType
		    || (type.IsGenericType && (type.GetGenericTypeDefinition() == typeof(Nullable<>))))
		{
			ArgumentNotNull(argName, (object)arg);
		}
	}

	[DebuggerHidden]
	[AssertionMethod]
    [PublicAPI]
	public static void ArgumentsNotNull(
		[NotNull, InvokerParameterName] string argName,
		[AssertionCondition(AssertionConditionType.IS_NOT_NULL), InstantHandle] IEnumerable argValue )
	{
// ReSharper disable PossibleMultipleEnumeration
		ArgumentNotNull( argName, argValue ) ;
// ReSharper restore PossibleMultipleEnumeration

		if( argValue.Cast<object>( ).Any( obj => obj == null ) )
		{
			throw new ArgumentException( @"Argument cannot contain a null value.", argName ) ;
		}
	}

	[DebuggerHidden]
	[AssertionMethod]
    [PublicAPI]
	public static void StringArgumentNotEmpty(
		[NotNull, InvokerParameterName] string argName,
		[AssertionCondition(AssertionConditionType.IS_NOT_NULL)] string argValue )
	{
		ArgumentNotNull( argName, argValue ) ;

		if( argValue.Length == 0 )
		{
			throw new ArgumentException( @"Argument cannot be zero length.", argName ) ;
		}
	}

	[DebuggerHidden]
	[AssertionMethod]
    [PublicAPI]
	public static void StringArgumentNotNullOrEmpty(
		[NotNull, InvokerParameterName] string argName,
		[AssertionCondition(AssertionConditionType.IS_NOT_NULL)] string argValue )
	{
		ArgumentNotNull( argName, argValue ) ;
		StringArgumentNotEmpty( argName, argValue ) ;
	}
}