Unable to write to JSONB column #1539

@nviktor

Description

Hi!
Having the same issue as #432 .

Can not insert value to a table with jsonb column (tried json also).
Insert code looks like this:

await _db.RequestLogs.InsertAsync(() =>
                new RequestLog
                    RequestBody = JsonConvert.SerializeObject(requestBody),
                });

pg logs:

2019-01-13 17:44:35.723 MSK [16200] ERROR:  42804: column "request_body" is of type jsonb but expression is of type text at character 129
2019-01-13 17:44:35.723 MSK [16200] STATEMENT:  INSERT INTO clear_junction.request_log
		request_body
	VALUES

Interesting, that it is ok to insert with constant:

await _db.RequestLogs.InsertAsync(() =>
                new RequestLog
                    RequestBody = "{""Body"": ""body value""}",
                });

linq2db version: 2.6.1
Database Server: PostgreSQL 11.1
Database Provider: Npgsql 4.0.4
Operating system: Windows 10
Framework version: .NET Core 2.1