On accessing chains of potentially null properties

NotNull.cs

using System;
using System.Collections.Generic;
using System.Linq.Expressions;
using System.Reflection;
 
namespace Helpers {
    public static class NotNull {
        public static TProp Get<TSource, TProp>(this TSource source, Expression<Func<TSource, TProp>> property) where TSource : class {
            if (source == null) return default(TProp);
            var current = property.Body;
            var properties = new List<PropertyInfo>();
            while (!(current is ParameterExpression)) {
                var memberExpression = current as MemberExpression;
                if (memberExpression == null || !(memberExpression.Member is PropertyInfo)) {
                    throw new InvalidOperationException("All members in the expression must be properties.");
                }
                properties.Add((PropertyInfo)memberExpression.Member);
                current = memberExpression.Expression;
            }
            properties.Reverse();
            object currentValue = source;
            foreach (var propertyInfo in properties) {
                if (currentValue == null) return default(TProp);
                currentValue = propertyInfo.GetValue(currentValue);
            }
            return (TProp) currentValue;
        }
    }
}