diff --git a/src/server/routes/clade_cumulus.jl b/src/server/routes/clade_cumulus.jl
index f7f81706..d140cda6 100644
--- a/src/server/routes/clade_cumulus.jl
+++ b/src/server/routes/clade_cumulus.jl
@@ -190,6 +190,15 @@ end
 end
 
 @post "/api/v1/studies/{study}/runs/{run}/clade-cumulus" function(req::HTTP.Request, study::String, run::String)
+    try
+        return _clade_cumulus_post_impl(req, study, run)
+    catch e
+        @error "clade-cumulus request failed" exception = (e, catch_backtrace())
+        return json_error(500, "clade_cumulus_failed", sprint(showerror, e))
+    end
+end
+
+function _clade_cumulus_post_impl(req::HTTP.Request, study::String, run::String)
     group = _req_group(req)
     err = _validate_run_request(study, run)
     !isnothing(err) && return err
diff --git a/src/server/routes/trees.jl b/src/server/routes/trees.jl
index beec713a..2d1cd348 100644
--- a/src/server/routes/trees.jl
+++ b/src/server/routes/trees.jl
@@ -14,8 +14,8 @@ const _TREE_MAX_BYTES  = 50 * 1024 * 1024
 const _VIEW_MAX_BYTES  = 5 * 1024 * 1024
 const _tree_view_lock  = ReentrantLock()
 
-_trees_dir(study::String) = joinpath(ServerState.projects_dir(), study, "trees")
-_tree_view_path(study::String, file::String) = joinpath(_trees_dir(study), ".views", file * ".json")
+_trees_dir(study::AbstractString) = joinpath(ServerState.projects_dir(), study, "trees")
+_tree_view_path(study::AbstractString, file::AbstractString) = joinpath(_trees_dir(study), ".views", file * ".json")
 
 _tree_format(file::AbstractString) = endswith(lowercase(file), ".jplace") ? "jplace" : "newick"
 
@@ -23,12 +23,12 @@ function _valid_tree_file(file::AbstractString)::Bool
     _valid_name(file) && any(ext -> endswith(lowercase(file), ext), _TREE_EXTENSIONS)
 end
 
-function _study_exists(study::String)::Bool
+function _study_exists(study::AbstractString)::Bool
     _valid_name(study) &&
         (isdir(joinpath(ServerState.projects_dir(), study)) || study in _study_names())
 end
 
-function _tree_request_error(study::String, file::Union{String,Nothing}=nothing)
+function _tree_request_error(study::AbstractString, file::Union{AbstractString,Nothing}=nothing)
     _study_exists(study) || return json_error(404, "study_not_found", "Study '$study' not found")
     isnothing(file) && return nothing
     _valid_tree_file(file) || return json_error(400, "invalid_name",
@@ -36,7 +36,7 @@ function _tree_request_error(study::String, file::Union{String,Nothing}=nothing)
     nothing
 end
 
-function _tree_listing(study::String)
+function _tree_listing(study::AbstractString)
     dir = _trees_dir(study)
     isdir(dir) || return NamedTuple[]
     files = sort(filter(f -> _valid_tree_file(f) && isfile(joinpath(dir, f)), readdir(dir)))