❔ How do I make part of a Linq query optional?

var newInfo = from ops in _radanContext.RouteCardOps
              join rc in _radanContext.RouteCards on ops.RouteNo equals rc.RouteNo
              join con in _radanContext.Contracts on rc.ContractNo equals con.ContractNo
              join parts in _radanContext.Parts on new { rc.PartNum, rc.Issue } equals new { parts.PartNum, parts.Issue }
              select new CompletedJobResult
              {
                  RouteNo = rc.RouteNo,
                  Seq = ops.Seq,
                  OpCode = ops.OpCode,
                  Issue = rc.Issue,
                  Description = ops.RouteDesc,
                  BatchQty = rc.BatchQty,
                  Qtycomplete = ops.QtyComplete,
                  ContractNo = con.ContractNo,
                  CustCode = con.CustCode,
                  PartNum = parts.Description,
                  BatchNo = rc.BatchNo
              };