diff --git a/src/slic3r/GUI/AppConfig.hpp b/src/slic3r/GUI/AppConfig.hpp
index 58e04433bc..c1c4607ec1 100644
--- a/src/slic3r/GUI/AppConfig.hpp
+++ b/src/slic3r/GUI/AppConfig.hpp
@@ -5,6 +5,8 @@
 #include <map>
 #include <string>
 
+#include <boost/algorithm/string/trim_all.hpp>
+
 #include "libslic3r/Config.hpp"
 #include "libslic3r/Semver.hpp"
 
@@ -52,7 +54,13 @@ public:
 	std::string 		get(const std::string &key) const
 		{ std::string value; this->get("", key, value); return value; }
 	void			    set(const std::string &section, const std::string &key, const std::string &value)
-	{ 
+	{
+#ifndef _NDEBUG
+		std::string key_trimmed = key;
+		boost::trim_all(key_trimmed);
+		assert(key_trimmed == key);
+		assert(! key_trimmed.empty());
+#endif _NDEBUG
 		std::string &old = m_storage[section][key];
 		if (old != value) {
 			old = value;
diff --git a/src/slic3r/GUI/ConfigWizard.cpp b/src/slic3r/GUI/ConfigWizard.cpp
index e66922630d..ac4357a2e2 100644
--- a/src/slic3r/GUI/ConfigWizard.cpp
+++ b/src/slic3r/GUI/ConfigWizard.cpp
@@ -1926,6 +1926,7 @@ void ConfigWizard::priv::update_presets_in_config(const std::string& section, co
     const PresetAliases& aliases = section == AppConfig::SECTION_FILAMENTS ? aliases_fff : aliases_sla;
 
     auto update = [this, add](const std::string& s, const std::string& key) {
+    	assert(! s.empty());
         if (add)
             appconfig_new.set(s, key, "1");
         else
diff --git a/src/slic3r/GUI/Preset.cpp b/src/slic3r/GUI/Preset.cpp
index b5d6392f93..28c959b692 100644
--- a/src/slic3r/GUI/Preset.cpp
+++ b/src/slic3r/GUI/Preset.cpp
@@ -189,6 +189,9 @@ VendorProfile VendorProfile::from_ini(const ptree &tree, const boost::filesystem
             	default_materials_field = section.second.get<std::string>("default_filaments", "");
             if (Slic3r::unescape_strings_cstyle(default_materials_field, model.default_materials)) {
             	Slic3r::sort_remove_duplicates(model.default_materials);
+            	if (! model.default_materials.empty() && model.default_materials.front().empty())
+            		// An empty material was inserted into the list of default materials. Remove it.
+            		model.default_materials.erase(model.default_materials.begin());
             } else {
                 BOOST_LOG_TRIVIAL(error) << boost::format("Vendor bundle: `%1%`: Malformed default_materials field: `%2%`") % id % default_materials_field;
             }