Filter empty children before performing minkowski sum. Fixes #1196

src/GeometryEvaluator.cc

@@ -123,7 +123,15 @@ GeometryEvaluator::ResultObject GeometryEvaluator::applyToChildren3D(const Abstr
 	// Only one child -> this is a noop
 	if (children.size() == 1) return ResultObject(children.front().second);
 
-	if (op == OPENSCAD_MINKOWSKI) return ResultObject(CGALUtils::applyMinkowski(children));
+	if (op == OPENSCAD_MINKOWSKI) {
+		Geometry::ChildList actualchildren;
+		BOOST_FOREACH(const Geometry::ChildItem &item, children) {
+			if (!item.second->isEmpty()) actualchildren.push_back(item);
+		}
+		if (actualchildren.empty()) return ResultObject();
+		if (actualchildren.size() == 1) return ResultObject(actualchildren.front().second);
+		return ResultObject(CGALUtils::applyMinkowski(actualchildren));
+	}
 
 	CGAL_Nef_polyhedron *N = CGALUtils::applyOperator(children, op);
 	// FIXME: Clarify when we can return NULL and what that means

src/cgalutils.cc

@@ -207,6 +207,9 @@ namespace CGALUtils {
 		return visited.size() == p.size_of_facets();
 	}
 
+	/*!
+		children cannot contain NULL objects
+	*/
 	Geometry const * applyMinkowski(const Geometry::ChildList &children)
 	{
 		CGAL::Timer t,t_tot;

testdata/scad/bugs/issue1196.scad

@@ -7,3 +7,14 @@ minkowski() {
     import("notfound.dxf");
   }
 }
+
+minkowski() {
+  linear_extrude() {
+    import("notfound.dxf");
+  }
+  linear_extrude() {
+    import("notfound.dxf");
+  }
+  cube();
+  cube();
+}