Fluent Validation helper methods to get errors for specific property

FluentValidationExtensions.cs

using System;
using System.Linq;
using System.Linq.Expressions;
using System.Resources;
using System.Web.Mvc;

using FluentValidation.Results;

namespace Helpers
{
  public static class FluentValidationHelper
  {
    // set your own resources
    private static readonly ResourceManager DefaultResourceManager = ValidationMessagesResources.ResourceManager;

    public static string GetErrorMessageByPropertyName<T>(this ValidationResult validationResult, Expression<Func<T, object>> property)
    {
      return GetErrorMessageByPropertyName(validationResult, property, DefaultResourceManager);
    }

    public static string GetErrorMessageByPropertyName<T>(this ValidationResult validationResult, Expression<Func<T, object>> property, ResourceManager resourceManager)
    {
      string propertyName = GetPropertyName(property);

      var validationFailure = validationResult.Errors.FirstOrDefault(x => x.PropertyName == propertyName);

      return validationFailure == null ? null : GetErrorMessage(validationFailure);
    }

    public static JsonResult GetJsonErrorMessageByPropertyName<T>(this ValidationResult validationResult, Expression<Func<T, object>> property)
    {
      return GetJsonErrorMessageByPropertyName(validationResult, property, DefaultResourceManager);
    }
    
    public static JsonResult GetJsonErrorMessageByPropertyName<T>(this ValidationResult validationResult, Expression<Func<T, object>> property, ResourceManager resourceManager)
    {
      var errorMessage = GetErrorMessageByPropertyName(validationResult, property, resourceManager);

      object data = errorMessage == null ? true : (object)errorMessage;

      return new JsonResult
      {
        Data = data,
        ContentType = null,
        ContentEncoding = null,
        JsonRequestBehavior = JsonRequestBehavior.AllowGet
      };
    }

    private static string GetPropertyName<T>(Expression<Func<T, object>> property)
    {
      var memberExpression = property.Body as MemberExpression;

      if (memberExpression != null)
      {
        return memberExpression.Member.Name;
      }

      var unaryExpression = property.Body as UnaryExpression;

      if (unaryExpression != null)
      {
        memberExpression = unaryExpression.Operand as MemberExpression;

        if (memberExpression != null)
        {
          return memberExpression.Member.Name;
        }
      }

      throw new InvalidOperationException("Coudln't get argument name from expression.");
    }

    private static string GetErrorMessage(ValidationFailure validationFailure)
    {
      var validationData = validationFailure.CustomState as ValidationData;

      return validationData != null
        ? ValidationMessagesResources.ResourceManager.GetString(validationData.ResourceKey)
        : validationFailure.ErrorMessage;
    }
  }
}