Tests: Add unit test to explore a null shape

tests/src/Mod/Part/App/TopoDS_Shape.cpp

@@ -3,8 +3,10 @@
 #include <gtest/gtest.h>
 #include <BRepBuilderAPI_MakeEdge.hxx>
 #include <Standard_TypeMismatch.hxx>
+#include <TopExp_Explorer.hxx>
 #include <TopoDS.hxx>
 #include <TopoDS_Edge.hxx>
+#include <TopoDS_Face.hxx>
 #include <TopoDS_Vertex.hxx>
 
 // NOLINTBEGIN
@@ -34,5 +36,12 @@ TEST(TopoDS_Shape, TestCastNullEdge)
     EXPECT_TRUE(vertex.IsNull());
 }
 
+TEST(TopoDS_Shape, TestExploreNullShape)
+{
+    TopoDS_Face face;
+    TopExp_Explorer xp(face, TopAbs_FACE);
+    EXPECT_FALSE(xp.More());
+}
+
 // clang-format on
 // NOLINTEND