diff --git a/packages/biu/include/biu/yaml.tpp b/packages/biu/include/biu/yaml.tpp
index 59e150da..556e8763 100644
--- a/packages/biu/include/biu/yaml.tpp
+++ b/packages/biu/include/biu/yaml.tpp
@@ -41,7 +41,7 @@ namespace YAML
   template <biu::SpecializationOf<std::optional> Optional> bool convert<Optional>::decode
     (const Node& node, Optional& optional)
   {
-    if (node.IsNull() || !node.IsDefined()) optional = std::nullopt;
+    if (!node.IsDefined() || node.IsNull()) optional = std::nullopt;
     else
     {
       typename Optional::value_type value;
diff --git a/packages/matplotplusplus.nix b/packages/matplotplusplus.nix
index 4a3f30f9..31963aea 100644
--- a/packages/matplotplusplus.nix
+++ b/packages/matplotplusplus.nix
@@ -7,7 +7,7 @@
   inherit src;
   cmakeFlags =
   [
-    "-DMATPLOTPP_BUILD_EXAMPLES=OFF"
+    "-DBUILD_SHARED_LIBS=ON" "-DMATPLOTPP_BUILD_SHARED_LIBS=ON" "-DMATPLOTPP_BUILD_EXAMPLES=OFF"
     "-DMATPLOTPP_WITH_SYSTEM_NODESOUP=ON" "-DMATPLOTPP_WITH_SYSTEM_CIMG=ON"
     "-DMATPLOTPP_BUILD_EXPERIMENTAL_OPENGL_BACKEND=ON" "-DGLAD_REPRODUCIBLE=ON"
   ];
diff --git a/packages/ufo/CMakeLists.txt b/packages/ufo/CMakeLists.txt
index 7c2441a1..ac4eef60 100644
--- a/packages/ufo/CMakeLists.txt
+++ b/packages/ufo/CMakeLists.txt
@@ -14,6 +14,9 @@ find_package(Matplot++ REQUIRED)
 find_package(biu REQUIRED)
 find_package(Threads REQUIRED)
 
+# matplot++ requires glad but does not find it
+find_package(glad REQUIRED)
+
 add_executable(ufo src/fold.cpp src/unfold.cpp src/plot.cpp src/main.cpp)
 target_include_directories(ufo PRIVATE ${PROJECT_SOURCE_DIR}/include)
 target_link_libraries(ufo PRIVATE TBB::tbb Matplot++::matplot Matplot++::matplot_opengl biu::biu)
diff --git a/packages/ufo/test/unfold/README.md b/packages/ufo/test/unfold/README.md
deleted file mode 100644
index e89192c9..00000000
--- a/packages/ufo/test/unfold/README.md
+++ /dev/null
@@ -1,2 +0,0 @@
-在 4H-SiC 超胞中，存在一个 C 空位，计算它的声子。
-