`no method matching (::Colon)(::Int64, ::Nothing)` when trying to solve a constrained problem with `Optimization.LBFGS`

[ForceBru]

Describe the bug 🐞

MethodError: no method matching (::Colon)(::Int64, ::Nothing) pops up from within the Optimization.jl package.

Expected behavior

The documentation of LBFGS says that LBFGS supports constrained problems:

This can also handle arbitrary non-linear constraints through a Augmented Lagrangian method with bounds constraints described in 17.4 of Numerical Optimization by Nocedal and Wright. Thus serving as a general-purpose nonlinear optimization solver available directly in Optimization.jl.

So I expect the code to produce a solution instead of an error.

Minimal Reproducible Example 👇

julia> using Optimization; import ForwardDiff

julia> rosenbrock(u, p) = (p[1] - u[1])^2 + p[2] * (u[2] - u[1]^2)^2;

julia> let
       p = [1.0, 100.0]
       function cons!(out, x, p) out[1]=sum(x); end
       optf = OptimizationFunction(rosenbrock, AutoForwardDiff(), cons=cons!)
       prob = OptimizationProblem(optf, [-1,1.], p, lcons=[0.0], ucons=[0.0])

       sol = solve(prob, Optimization.LBFGS())
       end

Error & Stacktrace ⚠️

ERROR: MethodError: no method matching (::Colon)(::Int64, ::Nothing)
The function `Colon()` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  (::Colon)(::T, ::Any, ::T) where T<:Real
   @ Base range.jl:50
  (::Colon)(::A, ::Any, ::C) where {A<:Real, C<:Real}
   @ Base range.jl:10
  (::Colon)(::T, ::Any, ::T) where T
   @ Base range.jl:49
  ...

Stacktrace:
 [1] __solve(cache::OptimizationCache{…})
   @ Optimization ~/.julia/packages/Optimization/hfEs4/src/lbfgsb.jl:176
 [2] solve!(cache::OptimizationCache{…})
   @ SciMLBase ~/.julia/packages/SciMLBase/DbVzk/src/solve.jl:228
 [3] solve(::OptimizationProblem{…}, ::Optimization.LBFGS; kwargs::@Kwargs{})
   @ SciMLBase ~/.julia/packages/SciMLBase/DbVzk/src/solve.jl:130
 [4] solve(::OptimizationProblem{…}, ::Optimization.LBFGS)
   @ SciMLBase ~/.julia/packages/SciMLBase/DbVzk/src/solve.jl:127
 [5] top-level scope
   @ REPL[9]:8

Environment (please complete the following information):

• Output of using Pkg; Pkg.status()

Status `/tmp/jl_SVKYUo/Project.toml`
  [f6369f11] ForwardDiff v1.0.1
  [7f7a1694] Optimization v4.4.0

• Output of using Pkg; Pkg.status(; mode = PKGMODE_MANIFEST)

Status `/tmp/jl_SVKYUo/Manifest.toml`
  [47edcb42] ADTypes v1.15.0
  [1520ce14] AbstractTrees v0.4.5
  [7d9f7c33] Accessors v0.1.42
  [79e6a3ab] Adapt v4.3.0
  [4fba245c] ArrayInterface v7.19.0
  [38540f10] CommonSolve v0.2.4
  [bbf7d656] CommonSubexpressions v0.3.1
  [a33af91c] CompositionsBase v0.1.2
  [88cd18e8] ConsoleProgressMonitor v0.1.2
  [187b0558] ConstructionBase v1.6.0
  [a8cc5b0e] Crayons v4.1.1
  [9a962f9c] DataAPI v1.16.0
  [e2d170a0] DataValueInterfaces v1.0.0
  [163ba53b] DiffResults v1.1.0
  [b552c78f] DiffRules v1.15.1
  [a0c0ee7d] DifferentiationInterface v0.7.3
  [ffbed154] DocStringExtensions v0.9.5
  [4e289a0a] EnumX v1.0.5
  [e2ba6199] ExprTools v0.1.10
  [55351af7] ExproniconLite v0.10.14
  [9aa1b823] FastClosures v0.3.2
  [1a297f60] FillArrays v1.13.0
  [f6369f11] ForwardDiff v1.0.1
  [069b7b12] FunctionWrappers v1.1.3
  [77dc65aa] FunctionWrappersWrappers v0.1.3
  [46192b85] GPUArraysCore v0.2.0
  [3587e190] InverseFunctions v0.1.17
  [92d709cd] IrrationalConstants v0.2.4
  [82899510] IteratorInterfaceExtensions v1.0.0
  [692b3bcd] JLLWrappers v1.7.1
  [ae98c720] Jieko v0.2.1
  [5be7bae1] LBFGSB v0.4.1
  [b964fa9f] LaTeXStrings v1.4.0
  [1d6d02ad] LeftChildRightSiblingTrees v0.2.1
  [2ab3a3ac] LogExpFunctions v0.3.29
  [e6f89c97] LoggingExtras v1.1.0
  [1914dd2f] MacroTools v0.5.16
  [2e0e35c7] Moshi v0.3.7
  [77ba4419] NaNMath v1.1.3
  [7f7a1694] Optimization v4.4.0
  [bca83a33] OptimizationBase v2.10.0
  [bac558e1] OrderedCollections v1.8.1
  [90014a1f] PDMats v0.11.35
⌅ [aea7be01] PrecompileTools v1.2.1
  [21216c6a] Preferences v1.4.3
  [08abe8d2] PrettyTables v2.4.0
  [33c8b6b6] ProgressLogging v0.1.5
  [92933f4c] ProgressMeter v1.10.4
  [3cdcf5f2] RecipesBase v1.3.4
  [731186ca] RecursiveArrayTools v3.36.0
  [189a3867] Reexport v1.2.2
  [ae029012] Requires v1.3.1
  [7e49a35a] RuntimeGeneratedFunctions v0.5.15
  [0bca4576] SciMLBase v2.105.0
  [c0aeaf25] SciMLOperators v1.4.0
  [53ae85a6] SciMLStructures v1.7.0
  [9f842d2f] SparseConnectivityTracer v1.0.0
  [0a514795] SparseMatrixColorings v0.4.21
  [276daf66] SpecialFunctions v2.5.1
  [1e83bf80] StaticArraysCore v1.4.3
  [10745b16] Statistics v1.11.1
  [892a3eda] StringManipulation v0.4.1
  [2efcf032] SymbolicIndexingInterface v0.3.42
  [3783bdb8] TableTraits v1.0.1
  [bd369af6] Tables v1.12.1
  [5d786b92] TerminalLoggers v0.1.7
  [81d17ec3] L_BFGS_B_jll v3.0.1+0
  [efe28fd5] OpenSpecFun_jll v0.5.6+0
  [0dad84c5] ArgTools v1.1.2
  [56f22d72] Artifacts v1.11.0
  [2a0f44e3] Base64 v1.11.0
  [ade2ca70] Dates v1.11.0
  [8ba89e20] Distributed v1.11.0
  [f43a241f] Downloads v1.6.0
  [7b1f6079] FileWatching v1.11.0
  [b27032c2] LibCURL v0.6.4
  [76f85450] LibGit2 v1.11.0
  [8f399da3] Libdl v1.11.0
  [37e2e46d] LinearAlgebra v1.11.0
  [56ddb016] Logging v1.11.0
  [d6f4376e] Markdown v1.11.0
  [ca575930] NetworkOptions v1.2.0
  [44cfe95a] Pkg v1.11.0
  [de0858da] Printf v1.11.0
  [9a3f8284] Random v1.11.0
  [ea8e919c] SHA v0.7.0
  [9e88b42a] Serialization v1.11.0
  [6462fe0b] Sockets v1.11.0
  [2f01184e] SparseArrays v1.11.0
  [4607b0f0] SuiteSparse
  [fa267f1f] TOML v1.0.3
  [a4e569a6] Tar v1.10.0
  [cf7118a7] UUIDs v1.11.0
  [4ec0a83e] Unicode v1.11.0
  [e66e0078] CompilerSupportLibraries_jll v1.1.1+0
  [deac9b47] LibCURL_jll v8.6.0+0
  [e37daf67] LibGit2_jll v1.7.2+0
  [29816b5a] LibSSH2_jll v1.11.0+1
  [c8ffd9c3] MbedTLS_jll v2.28.6+0
  [14a3606d] MozillaCACerts_jll v2023.12.12
  [4536629a] OpenBLAS_jll v0.3.27+1
  [05823500] OpenLibm_jll v0.8.5+0
  [bea87d4a] SuiteSparse_jll v7.7.0+0
  [83775a58] Zlib_jll v1.2.13+1
  [8e850b90] libblastrampoline_jll v5.11.0+0
  [8e850ede] nghttp2_jll v1.59.0+0
  [3f19e933] p7zip_jll v17.4.0+2

• Output of versioninfo()

Julia Version 1.11.6
Commit 9615af0f269 (2025-07-09 12:58 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 8 × AMD Ryzen 5 3550H with Radeon Vega Mobile Gfx
  WORD_SIZE: 64
  LLVM: libLLVM-16.0.6 (ORCJIT, znver1)
Threads: 1 default, 0 interactive, 1 GC (on 8 virtual cores)

Additional context

The error seems to come from

Optimization.jl/src/lbfgsb.jl

Line 178 in 779fd17

for i in 1:maxiters

Looks like maxiters is nothing instead of an integer. This likely has to do with

Optimization.jl/src/lbfgsb.jl

Line 94 in 779fd17

maxiters = Optimization._check_and_convert_maxiters(cache.solver_args.maxiters)