julia> using Oceananigans

julia> grid = RectilinearGrid(topology=(Bounded, Bounded, Bounded), size=(4, 4, 4), extent=(1, 1, 1));

julia> boundary_conditions = FieldBoundaryConditions(top = GradientBoundaryCondition(1));

julia> b = CenterField(grid; boundary_conditions)
ERROR: MethodError: no method matching fill_halo_kernel!(::Oceananigans.BoundaryConditions.BottomAndTop, ::Oceananigans.BoundaryConditions.DefaultBoundaryCondition{…}, ::RectilinearGrid{…}, ::Symbol, ::Tuple{…}, ::OffsetArrays.OffsetArray{…}, ::Tuple{})

Closest candidates are:
  fill_halo_kernel!(::Oceananigans.BoundaryConditions.BottomAndTop, ::BoundaryCondition{<:Oceananigans.BoundaryConditions.MultiRegionCommunication}, ::Any, ::Any, ::Any, ::Any, ::Any)
   @ Oceananigans ~/repos/Oceananigans.jl/src/BoundaryConditions/fill_halo_kernels.jl:162
  fill_halo_kernel!(::Oceananigans.BoundaryConditions.BottomAndTop, ::Oceananigans.BoundaryConditions.DistributedCommunicationBoundaryCondition, ::Any, ::Any, ::Any, ::Any, ::Any)
   @ Oceananigans ~/repos/Oceananigans.jl/src/BoundaryConditions/fill_halo_kernels.jl:148
  fill_halo_kernel!(::Oceananigans.BoundaryConditions.BottomAndTop, ::BoundaryCondition{<:Oceananigans.BoundaryConditions.Periodic}, ::Any, ::Any, ::Any, ::Any, ::Any)
   @ Oceananigans ~/repos/Oceananigans.jl/src/BoundaryConditions/fill_halo_kernels.jl:132
  ...

Stacktrace:
  [1] fill_halo_kernels
    @ ~/repos/Oceananigans.jl/src/BoundaryConditions/fill_halo_kernels.jl:54 [inlined]
  [2] construct_boundary_conditions_kernels(bcs::FieldBoundaryConditions{…}, data::OffsetArrays.OffsetArray{…}, grid::RectilinearGrid{…}, loc::Tuple{…}, indices::Tuple{…})
    @ Oceananigans.BoundaryConditions ~/repos/Oceananigans.jl/src/BoundaryConditions/fill_halo_kernels.jl:19
  [3] #construct_regionally#82
    @ ~/repos/Oceananigans.jl/src/Utils/multi_region_transformation.jl:159 [inlined]
  [4] construct_regionally
    @ ~/repos/Oceananigans.jl/src/Utils/multi_region_transformation.jl:154 [inlined]
  [5] macro expansion
    @ ~/repos/Oceananigans.jl/src/Utils/multi_region_transformation.jl:244 [inlined]
  [6] (Field{…})(grid::RectilinearGrid{…}, data::OffsetArrays.OffsetArray{…}, bcs::FieldBoundaryConditions{…}, indices::Tuple{…}, op::Nothing, status::Nothing, buffers::Nothing)
    @ Oceananigans.Fields ~/repos/Oceananigans.jl/src/Fields/field.jl:35
  [7] Field
    @ ~/repos/Oceananigans.jl/src/Fields/field.jl:106 [inlined]
  [8] Field(loc::Tuple{…}, grid::RectilinearGrid{…}, T::DataType; indices::Tuple{…}, data::OffsetArrays.OffsetArray{…}, boundary_conditions::FieldBoundaryConditions{…}, operand::Nothing, status::Nothing)
    @ Oceananigans.Fields ~/repos/Oceananigans.jl/src/Fields/field.jl:196
  [9] CenterField
    @ ~/repos/Oceananigans.jl/src/Fields/field.jl:208 [inlined]