The following code used to function under the version of MongoDb.Driver v2.12.2. Since I have upgrade the driver to v2.19.2 the following returns always null, notwithstanding there is data there. Any suggestions? The problem is with the project method.

public async Task<IEnumerable<PortfolioIdentifiers>> GetPortfolio(Guid portfolioId)
      {
          return await this.documentCollection
              .Find(x => x.Portfolio== portfolioId)
              .Project(x => x.PortfolioIdentifiers)
              .FirstOrDefaultAsync();
      }