efcore: Union fails if one query has returned no results

Union fails if one query in the union returns no result. An InvalidOperationException is thrown with the message "When performing a set operation, both operands must have the same include operations. Investigation revealed that if one of the queries in the union is empty (returned no results) the union operation fails. In code example below any or the queries (1, 2, or 3) may return no results.

        public async Task<DelimitedList> AvailableClubsAsync(string clubMnemonic = null)
        {
            using var context = new PGSSqlServerContext();

            var query1 = context.Clubs.ForGolferAsync().Where(cl => cl.ClubMnemonic == clubMnemonic)
                                                                                   .Select(cl => new { cl.ClubMnemonic, Sequence = 0 });

            var query2 = context.Clubs.ForGolferAsync().Where(cl => !cl.Courses.Any())
                                                                                   .Select(cl => new { cl.ClubMnemonic, Sequence = 1 });

            var numberOfTees = await context.Tees.ForGolferAsync().CountAsync().ConfigureAwait(false);

            var query3 = context.Courses.ForGolferAsync().Where(co => co.ClubMnemonic != clubMnemonic)
                                                                                       .GroupBy(co => new { co.ClubMnemonic, co.CourseName })
                                                                                       .Where(g => (g.Count() < numberOfTees && g.Key.CourseName == null) || (g.Key.CourseName != null))
                                                                                       .Select(g => new { g.Key.ClubMnemonic, Sequence = 1 });

            var query = query1.Union(query2).Union(query3)
                                          .OrderBy(q => q.Sequence).ThenBy(q => q.ClubMnemonic)
                                          .Select(q => q.ClubMnemonic);

            return new DelimitedList(list: await query.ToListAsync());
        }

Further technical details

EF Core version: 3.1.1 Database provider: (e.g. Microsoft.EntityFrameworkCore.SqlServer) Target framework: (e.g. .NET Core 3.1) Operating system: Windows 10 IDE: (e.g. Visual Studio 2019 164…3)