EF. Required validation error for string fields raise without [Required] attribute

Problem:

When adding new item into EntityCollectionView raised the required validation for string fields, but for my purpose we should show it after validation on server side.

Actual behavior:

Here is code from metadata file:

[MetadataTypeAttribute(typeof(SomeEntityMetadata))]
public partial class SomeEntity
{
    [EntityName]
    internal sealed class SomeEntityMetadata
    {
        private SomeEntityMetadata()
        {
        }

        public long Id { get; set; }

        [EntityName(Name = "Name", OrderIndex = 2)]
        public string Name { get; set; }

        [EntityName(Name = "Data Type", OrderIndex = 1)]
        public string Type { get; set; }

    }
}

And a collection of this items binded to DataGrid in xaml:

<navigation:DataGridTemplateColumn CanUserReorder="True"
                                   CanUserSort="True"
                                   Header="Name"
                                   SortMemberPath="Name">
    <navigation:DataGridTemplateColumn.CellTemplate>
        <DataTemplate>
            <TextBlock VerticalAlignment="Center" Text="{Binding Name}"/>
        </DataTemplate>
    </navigation:DataGridTemplateColumn.CellTemplate>
    <navigation:DataGridTemplateColumn.CellEditingTemplate>
        <DataTemplate>
            <TextBox Text="{Binding Name, Mode=TwoWay}" Height="Auto"/>
        </DataTemplate>
    </navigation:DataGridTemplateColumn.CellEditingTemplate>
</navigation:DataGridTemplateColumn>
<navigation:DataGridTemplateColumn CanUserFilter="True"
                                         CanUserSort="True"
                                         Header="Type"
                                         SortMemberPath="Type">
    <navigation:DataGridTemplateColumn.CellTemplate>
        <DataTemplate>