SqlResult.DynamicParameters loses type information for nulls

[shokurov]

Here is the simple example showing the problem (even though it does not call SqlKata):

[Fact]
    public void Dapper_WithSqlServerFailsWithRegularBinaryNullable()
    {
        // Arrange
        using var connection = new SqlConnection(Fixture.ConnectionString);
        connection.Open();
        // This simulates what SqlKata Compiler does with typed parameters: it converts them into dictionary
        // SqlResult.NamedBindings thus losing the type information for null parameters
        var parametersObject = new Dictionary<string, object?>
        {
            // ReSharper disable once RedundantCast
            ["BinaryData"] = (byte[]?)null
        };
        // Act
        var action = () =>
            // ReSharper disable once AccessToDisposedClosure
            connection.Execute(
                "INSERT INTO NullableVarbinary (BinaryData) VALUES (@BinaryData)",
                parametersObject
            );
        // Assert
        action
            .Should()
            .Throw<SqlException>()
            .WithMessage(
                "Implicit conversion from data type nvarchar to varbinary(max) is not allowed. Use the CONVERT function to run this query."
            );
    }

The way the SqlResult.DynamicParameters are declared makes it impossible to pass null value while maintaining type information for Dapper to do its job mapping to DB type.

Since the class is declared in core library and used by all compilers, it's hard to work around this problem.

I would propose making NamedBindings an interface similar to Dapper.IDynamicParameters with implementation that could be replaced for a QueryFactory.