CompoundItem: rm return value; don't start from nullptr

GUI/Model/Sample/CompoundItem.cpp

@@ -86,7 +86,9 @@ void CompoundItem::readFrom(QXmlStreamReader* r)
 
             // particle
         } else if (tag == Tag::Particle) {
-            addItemWithParticleSelection(nullptr).readFrom(r, m_materials);
+	    PolyItem<ParticlesCatalog> p;
+	    p.readFrom(r, m_materials);
+	    m_particles.emplace_item_back(p.releaseItem());
             XML::gotoEndElementOfTag(r, tag);
 
             // compound groupbox: is expanded?
@@ -132,10 +134,9 @@ QVector<ItemWithParticles*> CompoundItem::itemsWithParticles() const
     return m_particles.toModifiableQVector();
 }
 
-PolyItem<ParticlesCatalog>& CompoundItem::addItemWithParticleSelection(ItemWithParticles* particle)
+void CompoundItem::addItemWithParticleSelection(ItemWithParticles* particle)
 {
     m_particles.emplace_item_back(particle);
-    return m_particles.back();
 }
 
 void CompoundItem::removeItemWithParticle(ItemWithParticles* particle)

GUI/Model/Sample/CompoundItem.h

@@ -33,7 +33,8 @@ public:
     std::unique_ptr<Compound> createCompound() const;
 
     QVector<ItemWithParticles*> itemsWithParticles() const;
-    PolyItem<ParticlesCatalog>& addItemWithParticleSelection(ItemWithParticles* particle);
+
+    void addItemWithParticleSelection(ItemWithParticles* particle);
     void removeItemWithParticle(ItemWithParticles* particle);
 
     QVector<ItemWithParticles*> containedItemsWithParticles() const override;