From 24d90e1a934b72ab8768caa2cefca2cd2a8c0af6 Mon Sep 17 00:00:00 2001
From: odow <o.dowson@gmail.com>
Date: Mon, 18 Aug 2025 11:37:41 +1200
Subject: [PATCH] [Utilities] fix a Utilities.AbstractModel with no constraints

---
 src/Utilities/model.jl                 |  6 +++---
 src/Utilities/struct_of_constraints.jl |  3 ++-
 test/Utilities/model.jl                | 10 ++++++++++
 3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/Utilities/model.jl b/src/Utilities/model.jl
index 5b6230010c..184488c3b8 100644
--- a/src/Utilities/model.jl
+++ b/src/Utilities/model.jl
@@ -369,10 +369,10 @@ end
 function MOI.get(
     model::AbstractModel{T},
     attr::MOI.ListOfConstraintTypesPresent,
-) where {T}
+)::Vector{Tuple{Type,Type}} where {T}
     return vcat(
-        MOI.get(model.constraints, attr)::Vector{Tuple{Type,Type}},
-        MOI.get(model.variables, attr)::Vector{Tuple{Type,Type}},
+        MOI.get(model.constraints, attr),
+        MOI.get(model.variables, attr),
     )
 end
 
diff --git a/src/Utilities/struct_of_constraints.jl b/src/Utilities/struct_of_constraints.jl
index 6ece6f383d..a376e24388 100644
--- a/src/Utilities/struct_of_constraints.jl
+++ b/src/Utilities/struct_of_constraints.jl
@@ -152,9 +152,10 @@ function MOI.get(
 end
 
 function MOI.is_empty(model::StructOfConstraints)
-    return mapreduce_constraints(&, model, true) do constrs
+    ret = mapreduce_constraints(&, model, true) do constrs
         return constrs === nothing || MOI.is_empty(constrs)
     end
+    return something(ret, true)
 end
 
 function MOI.empty!(model::StructOfConstraints)
diff --git a/test/Utilities/model.jl b/test/Utilities/model.jl
index 62d5d57a7e..10ef4b784c 100644
--- a/test/Utilities/model.jl
+++ b/test/Utilities/model.jl
@@ -617,6 +617,16 @@ function test_struct_of_constraints_by_set_types()
     return
 end
 
+MOI.Utilities.@model(EmptyModel, (), (), (), (), (), (), (), ())
+
+function test_empty_model()
+    model = EmptyModel{Float64}()
+    @test MOI.is_empty(model)
+    @test MOI.get(model, MOI.ListOfConstraintTypesPresent()) ==
+          Tuple{Type,Type}[]
+    return
+end
+
 end  # module
 
 TestModel.runtests()