diff --git a/Manifest.toml b/Manifest.toml
deleted file mode 100644
index a035dea5..00000000
--- a/Manifest.toml
+++ /dev/null
@@ -1,250 +0,0 @@
-# This file is machine-generated - editing it directly is not advised
-
-[[Arpack]]
-deps = ["Arpack_jll", "Libdl", "LinearAlgebra"]
-git-tree-sha1 = "2ff92b71ba1747c5fdd541f8fc87736d82f40ec9"
-uuid = "7d9fca2a-8960-54d3-9f78-7d1dccf2cb97"
-version = "0.4.0"
-
-[[Arpack_jll]]
-deps = ["Libdl", "OpenBLAS_jll", "Pkg"]
-git-tree-sha1 = "68a90a692ddc0eb72d69a6993ca26e2a923bf195"
-uuid = "68821587-b530-5797-8361-c406ea357684"
-version = "3.5.0+2"
-
-[[Base64]]
-uuid = "2a0f44e3-6c83-55bd-87e4-b1978d98bd5f"
-
-[[BinaryProvider]]
-deps = ["Libdl", "SHA"]
-git-tree-sha1 = "5b08ed6036d9d3f0ee6369410b830f8873d4024c"
-uuid = "b99e7846-7c00-51b0-8f62-c81ae34c0232"
-version = "0.5.8"
-
-[[CategoricalArrays]]
-deps = ["Compat", "DataAPI", "Future", "JSON", "Missings", "Printf", "Reexport", "Statistics", "Unicode"]
-git-tree-sha1 = "23d7324164c89638c18f6d7f90d972fa9c4fa9fb"
-uuid = "324d7699-5711-5eae-9e2f-1d82baa6b597"
-version = "0.7.7"
-
-[[Compat]]
-deps = ["Base64", "Dates", "DelimitedFiles", "Distributed", "InteractiveUtils", "LibGit2", "Libdl", "LinearAlgebra", "Markdown", "Mmap", "Pkg", "Printf", "REPL", "Random", "SHA", "Serialization", "SharedArrays", "Sockets", "SparseArrays", "Statistics", "Test", "UUIDs", "Unicode"]
-git-tree-sha1 = "a4839bd26e3e7f4869a4cf6c31f9f93f47aac7c5"
-uuid = "34da2185-b29b-5c13-b0c7-acf172513d20"
-version = "3.5.0"
-
-[[DataAPI]]
-git-tree-sha1 = "674b67f344687a88310213ddfa8a2b3c76cc4252"
-uuid = "9a962f9c-6df0-11e9-0e5d-c546b8b5ee8a"
-version = "1.1.0"
-
-[[DataStructures]]
-deps = ["InteractiveUtils", "OrderedCollections"]
-git-tree-sha1 = "b7720de347734f4716d1815b00ce5664ed6bbfd4"
-uuid = "864edb3b-99cc-5e75-8d2d-829cb0a9cfe8"
-version = "0.17.9"
-
-[[Dates]]
-deps = ["Printf"]
-uuid = "ade2ca70-3891-5945-98fb-dc099432e06a"
-
-[[DelimitedFiles]]
-deps = ["Mmap"]
-uuid = "8bb1440f-4735-579b-a4ab-409b98df4dab"
-
-[[Distributed]]
-deps = ["Random", "Serialization", "Sockets"]
-uuid = "8ba89e20-285c-5b6f-9357-94700520ee1b"
-
-[[Distributions]]
-deps = ["FillArrays", "LinearAlgebra", "PDMats", "Printf", "QuadGK", "Random", "SpecialFunctions", "Statistics", "StatsBase", "StatsFuns"]
-git-tree-sha1 = "6b19601c0e98de3a8964ed33ad73e130c7165b1d"
-uuid = "31c24e10-a181-5473-b8eb-7969acd0382f"
-version = "0.22.4"
-
-[[FillArrays]]
-deps = ["LinearAlgebra", "Random", "SparseArrays"]
-git-tree-sha1 = "fec413d4fc547992eb62a5c544cedb6d7853c1f5"
-uuid = "1a297f60-69ca-5386-bcde-b61e274b549b"
-version = "0.8.4"
-
-[[Future]]
-deps = ["Random"]
-uuid = "9fa8497b-333b-5362-9e8d-4d0656e87820"
-
-[[InteractiveUtils]]
-deps = ["Markdown"]
-uuid = "b77e0a4c-d291-57a0-90e8-8db25a27a240"
-
-[[JSON]]
-deps = ["Dates", "Mmap", "Parsers", "Unicode"]
-git-tree-sha1 = "b34d7cef7b337321e97d22242c3c2b91f476748e"
-uuid = "682c06a0-de6a-54ab-a142-c8b1cf79cde6"
-version = "0.21.0"
-
-[[LibGit2]]
-uuid = "76f85450-5226-5b5a-8eaa-529ad045b433"
-
-[[Libdl]]
-uuid = "8f399da3-3557-5675-b5ff-fb832c97cbdb"
-
-[[LinearAlgebra]]
-deps = ["Libdl"]
-uuid = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
-
-[[Logging]]
-uuid = "56ddb016-857b-54e1-b83d-db4d58db5568"
-
-[[MLJModelInterface]]
-deps = ["ScientificTypes"]
-git-tree-sha1 = "269deeabed43d68656c80fa57a83fb53ad202728"
-uuid = "e80e1ace-859a-464e-9ed9-23947d8ae3ea"
-version = "0.1.5"
-
-[[Markdown]]
-deps = ["Base64"]
-uuid = "d6f4376e-aef5-505a-96c1-9c027394607a"
-
-[[Missings]]
-deps = ["DataAPI"]
-git-tree-sha1 = "de0a5ce9e5289f27df672ffabef4d1e5861247d5"
-uuid = "e1d29d7a-bbdc-5cf2-9ac0-f12de2c33e28"
-version = "0.4.3"
-
-[[Mmap]]
-uuid = "a63ad114-7e13-5084-954f-fe012c677804"
-
-[[OpenBLAS_jll]]
-deps = ["Libdl", "Pkg"]
-git-tree-sha1 = "e2551d7c25d52f35b76d86a50917a3ba8988f519"
-uuid = "4536629a-c528-5b80-bd46-f80d51c5b363"
-version = "0.3.7+5"
-
-[[OpenSpecFun_jll]]
-deps = ["Libdl", "Pkg"]
-git-tree-sha1 = "65f672edebf3f4e613ddf37db9dcbd7a407e5e90"
-uuid = "efe28fd5-8261-553b-a9e1-b2916fc3738e"
-version = "0.5.3+1"
-
-[[OrderedCollections]]
-deps = ["Random", "Serialization", "Test"]
-git-tree-sha1 = "c4c13474d23c60d20a67b217f1d7f22a40edf8f1"
-uuid = "bac558e1-5e72-5ebc-8fee-abe8a469f55d"
-version = "1.1.0"
-
-[[PDMats]]
-deps = ["Arpack", "LinearAlgebra", "SparseArrays", "SuiteSparse", "Test"]
-git-tree-sha1 = "5f303510529486bb02ac4d70da8295da38302194"
-uuid = "90014a1f-27ba-587c-ab20-58faa44d9150"
-version = "0.9.11"
-
-[[Parsers]]
-deps = ["Dates", "Test"]
-git-tree-sha1 = "d112c19ccca00924d5d3a38b11ae2b4b268dda39"
-uuid = "69de0a69-1ddd-5017-9359-2bf0b02dc9f0"
-version = "0.3.11"
-
-[[Pkg]]
-deps = ["Dates", "LibGit2", "Libdl", "Logging", "Markdown", "Printf", "REPL", "Random", "SHA", "UUIDs"]
-uuid = "44cfe95a-1eb2-52ea-b672-e2afdf69b78f"
-
-[[Printf]]
-deps = ["Unicode"]
-uuid = "de0858da-6303-5e67-8744-51eddeeeb8d7"
-
-[[QuadGK]]
-deps = ["DataStructures", "LinearAlgebra"]
-git-tree-sha1 = "dc84e810393cfc6294248c9032a9cdacc14a3db4"
-uuid = "1fd47b50-473d-5c70-9696-f719f8f3bcdc"
-version = "2.3.1"
-
-[[REPL]]
-deps = ["InteractiveUtils", "Markdown", "Sockets"]
-uuid = "3fa0cd96-eef1-5676-8a61-b3b8758bbffb"
-
-[[Random]]
-deps = ["Serialization"]
-uuid = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
-
-[[Reexport]]
-deps = ["Pkg"]
-git-tree-sha1 = "7b1d07f411bc8ddb7977ec7f377b97b158514fe0"
-uuid = "189a3867-3050-52da-a836-e630ba90ab69"
-version = "0.2.0"
-
-[[Rmath]]
-deps = ["BinaryProvider", "Libdl", "Random", "Statistics"]
-git-tree-sha1 = "2bbddcb984a1d08612d0c4abb5b4774883f6fa98"
-uuid = "79098fc4-a85e-5d69-aa6a-4863f24498fa"
-version = "0.6.0"
-
-[[SHA]]
-uuid = "ea8e919c-243c-51af-8825-aaa63cd721ce"
-
-[[ScientificTypes]]
-git-tree-sha1 = "9c232034bbee8c53173cdce83787bf8968b09d31"
-uuid = "321657f4-b219-11e9-178b-2701a2544e81"
-version = "0.7.1"
-
-[[Serialization]]
-uuid = "9e88b42a-f829-5b0c-bbe9-9e923198166b"
-
-[[SharedArrays]]
-deps = ["Distributed", "Mmap", "Random", "Serialization"]
-uuid = "1a1011a3-84de-559e-8e89-a11a2f7dc383"
-
-[[Sockets]]
-uuid = "6462fe0b-24de-5631-8697-dd941f90decc"
-
-[[SortingAlgorithms]]
-deps = ["DataStructures", "Random", "Test"]
-git-tree-sha1 = "03f5898c9959f8115e30bc7226ada7d0df554ddd"
-uuid = "a2af1166-a08f-5f64-846c-94a0d3cef48c"
-version = "0.3.1"
-
-[[SparseArrays]]
-deps = ["LinearAlgebra", "Random"]
-uuid = "2f01184e-e22b-5df5-ae63-d93ebab69eaf"
-
-[[SpecialFunctions]]
-deps = ["OpenSpecFun_jll"]
-git-tree-sha1 = "e19b98acb182567bcb7b75bb5d9eedf3a3b5ec6c"
-uuid = "276daf66-3868-5448-9aa4-cd146d93841b"
-version = "0.10.0"
-
-[[StaticArrays]]
-deps = ["LinearAlgebra", "Random", "Statistics"]
-git-tree-sha1 = "5a3bcb6233adabde68ebc97be66e95dcb787424c"
-uuid = "90137ffa-7385-5640-81b9-e52037218182"
-version = "0.12.1"
-
-[[Statistics]]
-deps = ["LinearAlgebra", "SparseArrays"]
-uuid = "10745b16-79ce-11e8-11f9-7d13ad32a3b2"
-
-[[StatsBase]]
-deps = ["DataAPI", "DataStructures", "LinearAlgebra", "Missings", "Printf", "Random", "SortingAlgorithms", "SparseArrays", "Statistics"]
-git-tree-sha1 = "be5c7d45daa449d12868f4466dbf5882242cf2d9"
-uuid = "2913bbd2-ae8a-5f71-8c99-4fb6c76f3a91"
-version = "0.32.1"
-
-[[StatsFuns]]
-deps = ["Rmath", "SpecialFunctions"]
-git-tree-sha1 = "f290ddd5fdedeadd10e961eb3f4d3340f09d030a"
-uuid = "4c63d2b9-4356-54db-8cca-17b64c39e42c"
-version = "0.9.4"
-
-[[SuiteSparse]]
-deps = ["Libdl", "LinearAlgebra", "Serialization", "SparseArrays"]
-uuid = "4607b0f0-06f3-5cda-b6b1-a6196a1729e9"
-
-[[Test]]
-deps = ["Distributed", "InteractiveUtils", "Logging", "Random"]
-uuid = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
-
-[[UUIDs]]
-deps = ["Random", "SHA"]
-uuid = "cf7118a7-6976-5b1a-9a39-7adc72f591a4"
-
-[[Unicode]]
-uuid = "4ec0a83e-493e-50e2-b9ac-8f72acf5a8f5"
diff --git a/src/fit.jl b/src/fit.jl
index a0388329..ea02787f 100644
--- a/src/fit.jl
+++ b/src/fit.jl
@@ -214,7 +214,7 @@ function fit_evotree(params, X_train, Y_train;
     model, cache = init_evotree(params, X_train, Y_train)
     iter = 1
 
-    if params.metric != :none && !isnothing(X_eval)
+    if params.metric != :none && X_eval !== nothing
         pred_eval = predict(model.trees[1], X_eval, model.K)
     end
 
@@ -223,7 +223,7 @@ function fit_evotree(params, X_train, Y_train;
         grow_evotree!(model, cache)
         # callback function
         if params.metric != :none
-            if !isnothing(X_eval)
+            if X_eval !== nothing
                 predict!(pred_eval, model.trees[model.params.nrounds+1], X_eval)
                 metric_track.metric = eval_metric(Val{params.metric}(), pred_eval, Y_eval, params.α)
             else