Fixes:

  error: missing sentinel in function call

diff --git a/src/gui/gtk.h b/src/gui/gtk.h
index 8c1fc23..1a0638d 100644
--- a/src/gui/gtk.h
+++ b/src/gui/gtk.h
@@ -334,7 +334,7 @@ static inline void dtgtk_justify_notebook_tabs(GtkNotebook *notebook)
   for(gint i = 0; i < gtk_notebook_get_n_pages(notebook); ++i)
     gtk_container_child_set(GTK_CONTAINER(notebook),
                             gtk_notebook_get_nth_page(notebook, i),
-                            "tab-expand", TRUE, "tab-fill", TRUE, NULL);
+                            "tab-expand", TRUE, "tab-fill", TRUE, (char*)NULL);
 }
 
 // show a dialog box with 2 buttons in case some user interaction is required BEFORE dt's gui is initialised.
diff --git a/src/iop/lens.cc b/src/iop/lens.cc
index 41dc792..547acf7 100644
--- a/src/iop/lens.cc
+++ b/src/iop/lens.cc
@@ -1256,7 +1256,7 @@ void init_global(dt_iop_module_so_t *module)
     gchar *path = g_file_get_path(g_file_get_parent(file));
     g_object_unref(file);
 #ifdef LF_MAX_DATABASE_VERSION
-    gchar *sysdbpath = g_build_filename(path, "lensfun", "version_" STR(LF_MAX_DATABASE_VERSION), NULL);
+    gchar *sysdbpath = g_build_filename(path, "lensfun", "version_" STR(LF_MAX_DATABASE_VERSION), (char*)NULL);
 #endif
 
 #ifdef LF_0395
@@ -1277,7 +1277,7 @@ void init_global(dt_iop_module_so_t *module)
       fprintf(stderr, "[iop_lens]: could not load lensfun database in `%s'!\n", sysdbpath);
 #endif
       g_free(dt_iop_lensfun_db->HomeDataDir);
-      dt_iop_lensfun_db->HomeDataDir = g_build_filename(path, "lensfun", NULL);
+      dt_iop_lensfun_db->HomeDataDir = g_build_filename(path, "lensfun", (char*)NULL);
       if(dt_iop_lensfun_db->Load() != LF_NO_ERROR)
         fprintf(stderr, "[iop_lens]: could not load lensfun database in `%s'!\n", dt_iop_lensfun_db->HomeDataDir);
 #ifdef LF_MAX_DATABASE_VERSION