Some defensiveness against null shapes (should look into this better)

src/ifcgeom/kernels/opencascade/OpenCascadeKernel.cpp

@@ -280,6 +280,10 @@ bool IfcGeom::OpenCascadeKernel::convert_openings(const IfcUtil::IfcBaseEntity*
 		std::list<TopoDS_Shape> parts;
 
 		auto it3_shape = std::static_pointer_cast<OpenCascadeShape>(it3->Shape())->shape();
+		if (it3_shape.IsNull()) {
+			Logger::Error("Null operand");
+			continue;
+		}
 
 		bool is_multiple = it3_shape.ShapeType() == TopAbs_COMPOUND && TopoDS_Iterator(it3_shape).More() && util::is_nested_compound_of_solid(it3_shape);
 

src/ifcgeom/kernels/opencascade/boolean_result.cpp

@@ -123,6 +123,10 @@ bool OpenCascadeKernel::convert_impl(const taxonomy::boolean_result::ptr br, Con
 
 			for (auto& r : cr) {
 				auto S = std::static_pointer_cast<OpenCascadeShape>(r.Shape())->shape();
+				if (S.IsNull()) {
+					Logger::Error("Null operand");
+					continue;
+				}
 				gp_GTrsf trsf;
 				convert(r.Placement(), trsf);
 				// @todo it really confuses me why I cannot use Moved() here instead
@@ -155,7 +159,7 @@ bool OpenCascadeKernel::convert_impl(const taxonomy::boolean_result::ptr br, Con
 
 	TopoDS_Shape r;
 
-	if (a.ShapeType() == TopAbs_COMPOUND && TopoDS_Iterator(a).More() && util::is_nested_compound_of_solid(a)) {
+	if (br->operation == taxonomy::boolean_result::SUBTRACTION && !a.IsNull() && a.ShapeType() == TopAbs_COMPOUND && TopoDS_Iterator(a).More() && util::is_nested_compound_of_solid(a)) {
 		TopoDS_Compound C;
 		BRep_Builder B;
 		B.MakeCompound(C);

src/ifcgeom/kernels/opencascade/boolean_utils.cpp

@@ -981,7 +981,9 @@ bool IfcGeom::util::boolean_operation(const boolean_settings& settings, const To
 	if (Logger::LOG_NOTICE >= Logger::Verbosity()) {
 		PERF("preliminary manifoldness check");
 
-		Logger::Notice("Operand A is " + (is_manifold(a) ? ""s : "non-"s) + "manifold");
+		if (!a.IsNull()) {
+			Logger::Notice("Operand A is " + (is_manifold(a) ? ""s : "non-"s) + "manifold");
+		}
 
 		TopTools_ListIteratorOfListOfShape it(b);
 		for (int i = 0; it.More(); it.Next(), ++i) {