julia> FieldBoundaryConditions(grid, (Center, Center, Center); top = GradientBoundaryCondition(1))
ERROR: MethodError: no method matching default_prognostic_bc(::Bounded, ::Type{Center}, ::Oceananigans.BoundaryConditions.DefaultBoundaryCondition{BoundaryCondition{Oceananigans.BoundaryConditions.Flux, Nothing}})

Closest candidates are:
  default_prognostic_bc(::Flat, ::Any, ::Any)
   @ Oceananigans ~/repos/Oceananigans.jl/src/BoundaryConditions/field_boundary_conditions.jl:17
  default_prognostic_bc(::Oceananigans.Grids.FullyConnected, ::Any, ::Any)
   @ Oceananigans ~/repos/Oceananigans.jl/src/BoundaryConditions/field_boundary_conditions.jl:16
  default_prognostic_bc(::Bounded, ::Nothing, ::Any)
   @ Oceananigans ~/repos/Oceananigans.jl/src/BoundaryConditions/field_boundary_conditions.jl:27
  ...

Stacktrace:
 [1] _default_auxiliary_bc(topo::Bounded, loc::Type)
   @ Oceananigans.BoundaryConditions ~/repos/Oceananigans.jl/src/BoundaryConditions/field_boundary_conditions.jl:34
 [2] default_auxiliary_bc(grid::RectilinearGrid{…}, ::Val{…}, loc::Tuple{…})
   @ Oceananigans.BoundaryConditions ~/repos/Oceananigans.jl/src/BoundaryConditions/field_boundary_conditions.jl:40
 [3] top-level scope
   @ REPL[6]:1