Set nullptr in cpp not hpp - Linux want know the size of pimpl.

src/slic3r/GUI/Gizmos/GLGizmoEmboss.cpp

@@ -282,6 +282,7 @@ struct GLGizmoEmboss::GuiCfg: public ::GuiCfg{};
 
 GLGizmoEmboss::GLGizmoEmboss(GLCanvas3D &parent)
     : GLGizmoBase(parent, M_ICON_FILENAME, -2)
+    , m_gui_cfg(nullptr)
     , m_style_manager(m_imgui->get_glyph_ranges(), create_default_styles)
     , m_face_names(std::make_unique<Facenames>())
     , m_rotate_gizmo(parent, GLGizmoRotate::Axis::Z) // grab id = 2 (Z axis)

src/slic3r/GUI/Gizmos/GLGizmoEmboss.hpp

@@ -151,7 +151,7 @@ private:
     void remove_notification_not_valid_font();
 
     struct GuiCfg;
-    std::unique_ptr<const GuiCfg> m_gui_cfg = nullptr;
+    std::unique_ptr<const GuiCfg> m_gui_cfg;
 
     // Is open tree with advanced options
     bool m_is_advanced_edit_style = false;
@@ -167,7 +167,7 @@ private:
 
     // pImpl to hide implementation of FaceNames to .cpp file
     struct Facenames; // forward declaration
-    std::unique_ptr<Facenames> m_face_names = nullptr;
+    std::unique_ptr<Facenames> m_face_names;
 
     // Text to emboss
     std::string m_text; // Sequence of Unicode UTF8 symbols

src/slic3r/GUI/Gizmos/GLGizmoSVG.cpp

@@ -37,6 +37,7 @@ using namespace Slic3r::GUI::Emboss;
 
 GLGizmoSVG::GLGizmoSVG(GLCanvas3D &parent)
     : GLGizmoBase(parent, M_ICON_FILENAME, -3)
+    , m_gui_cfg(nullptr)
     , m_rotate_gizmo(parent, GLGizmoRotate::Axis::Z) // grab id = 2 (Z axis)
 {
     m_rotate_gizmo.set_group_id(0);

src/slic3r/GUI/Gizmos/GLGizmoSVG.hpp

@@ -110,7 +110,7 @@ private:
     bool on_mouse_for_translate(const wxMouseEvent &mouse_event);
     
     struct GuiCfg;
-    std::unique_ptr<const GuiCfg> m_gui_cfg = nullptr;
+    std::unique_ptr<const GuiCfg> m_gui_cfg;
 
     // actual selected only one volume - with emboss data
     ModelVolume *m_volume = nullptr;