diff --git a/src/nlp_expr.jl b/src/nlp_expr.jl
index 84b4c6f2bb3..373d63611a6 100644
--- a/src/nlp_expr.jl
+++ b/src/nlp_expr.jl
@@ -724,7 +724,7 @@ function Base.convert(
     if !iszero(x.constant) || isempty(args)
         push!(args, x.constant)
     end
-    if length(args) == 1
+    if length(args) == 1 && args[1] isa GenericNonlinearExpr{V}
         return args[1]
     end
     return GenericNonlinearExpr{V}(:+, args)
@@ -752,7 +752,7 @@ function Base.convert(
     if !iszero(x.aff.constant) || isempty(args)
         push!(args, x.aff.constant)
     end
-    if length(args) == 1
+    if length(args) == 1 && args[1] isa GenericNonlinearExpr{V}
         return args[1]
     end
     return GenericNonlinearExpr{V}(:+, args)
diff --git a/test/Kokako.jl b/test/Kokako.jl
index d780cb5e433..ffbd349b7e7 100644
--- a/test/Kokako.jl
+++ b/test/Kokako.jl
@@ -131,8 +131,10 @@ end
 function include_modules_to_test(dir::String, files::Vector{String})
     modules = Pair{String,Module}[]
     for file in files
-        @info "Loading $file"
-        push!(modules, file => Base.include(Main, joinpath(dir, file)))
+        if isfile(joinpath(dir, file))
+            @info "Loading $file"
+            push!(modules, file => Base.include(Main, joinpath(dir, file)))
+        end
     end
     return modules
 end
diff --git a/test/test_nlp_expr.jl b/test/test_nlp_expr.jl
index 747ce29d344..12132407b54 100644
--- a/test/test_nlp_expr.jl
+++ b/test/test_nlp_expr.jl
@@ -233,8 +233,8 @@ function test_extension_aff_expr_convert(
     model = ModelType()
     @variable(model, x)
     _to_string(x) = string(convert(GenericNonlinearExpr{VariableRefType}, x))
-    @test _to_string(AffExpr(0.0)) == "0.0"
-    @test _to_string(AffExpr(1.0)) == "1.0"
+    @test _to_string(AffExpr(0.0)) == "+(0.0)"
+    @test _to_string(AffExpr(1.0)) == "+(1.0)"
     @test _to_string(x + 1) == "x + 1.0"
     @test _to_string(2x + 1) == "(2.0 * x) + 1.0"
     @test _to_string(2x) == "2.0 * x"
@@ -248,8 +248,8 @@ function test_extension_quad_expr_convert(
     model = ModelType()
     @variable(model, x)
     _to_string(x) = string(convert(GenericNonlinearExpr{VariableRefType}, x))
-    @test _to_string(QuadExpr(AffExpr(0.0))) == "0.0"
-    @test _to_string(QuadExpr(AffExpr(1.0))) == "1.0"
+    @test _to_string(QuadExpr(AffExpr(0.0))) == "+(0.0)"
+    @test _to_string(QuadExpr(AffExpr(1.0))) == "+(1.0)"
     @test _to_string(x^2 + 1) == "(x * x) + 1.0"
     @test _to_string(2x^2 + 1) == "(2.0 * x * x) + 1.0"
     @test _to_string(2x^2) == "2.0 * x * x"
@@ -1010,4 +1010,13 @@ function test_printing_truncation()
     return
 end
 
+function test_convert_vector_aff_expr()
+    model = Model()
+    @variable(model, x)
+    @test [sin(x), x] isa Vector{NonlinearExpr}
+    @test [sin(x), x + 1] isa Vector{NonlinearExpr}
+    @test [sin(x), convert(AffExpr, x)] isa Vector{NonlinearExpr}
+    return
+end
+
 end  # module