diff --git a/library/terrain_library.cpp b/library/terrain_library.cpp
index fcb9324..9188b71 100644
--- a/library/terrain_library.cpp
+++ b/library/terrain_library.cpp
@@ -161,13 +161,13 @@ bool TerrainLibrary::_supports_caching() {
 
 //Materials
 Ref<Material> TerrainLibrary::material_get(const int index) {
-	ERR_FAIL_INDEX_V(index, _materials.size(), Ref<Material>(NULL));
+	ERR_FAIL_INDEX_V(index, _materials.size(), Ref<Material>());
 
 	return _materials[index];
 }
 
 Ref<Material> TerrainLibrary::material_lod_get(const int index) {
-	ERR_FAIL_COND_V(_materials.size() == 0, Ref<Material>(NULL));
+	ERR_FAIL_COND_V_MSG(_materials.size() == 0, Ref<Material>(), "Error! You should to add at least one material to TerrainLibrary! (By default it will use up to 5. See VoxelWorldDefault::_create_chunk().)");
 
 	if (index < 0) {
 		return _materials[0];
@@ -241,13 +241,13 @@ void TerrainLibrary::materials_set(const Vector<Variant> &materials) {
 
 //Liquid Materials
 Ref<Material> TerrainLibrary::liquid_material_get(const int index) {
-	ERR_FAIL_INDEX_V(index, _liquid_materials.size(), Ref<Material>(NULL));
+	ERR_FAIL_INDEX_V(index, _liquid_materials.size(), Ref<Material>());
 
 	return _liquid_materials[index];
 }
 
 Ref<Material> TerrainLibrary::liquid_material_lod_get(const int index) {
-	ERR_FAIL_COND_V(_materials.size() == 0, Ref<Material>(NULL));
+	ERR_FAIL_COND_V_MSG(_liquid_materials.size() == 0, Ref<Material>(), "Error! You should to add at least one liquid to TerrainLibrary! (By default it will use up to 5. See VoxelWorldDefault::_create_chunk().)");
 
 	if (index < 0) {
 		return _liquid_materials[0];
@@ -321,13 +321,13 @@ void TerrainLibrary::liquid_materials_set(const Vector<Variant> &materials) {
 
 //Prop Materials
 Ref<Material> TerrainLibrary::prop_material_get(const int index) {
-	ERR_FAIL_INDEX_V(index, _prop_materials.size(), Ref<Material>(NULL));
+	ERR_FAIL_INDEX_V(index, _prop_materials.size(), Ref<Material>());
 
 	return _prop_materials[index];
 }
 
 Ref<Material> TerrainLibrary::prop_material_lod_get(const int index) {
-	ERR_FAIL_COND_V(_prop_materials.size() == 0, Ref<Material>(NULL));
+	ERR_FAIL_COND_V_MSG(_prop_materials.size() == 0, Ref<Material>(), "Error! You should to add at least one material to TerrainLibrary!");
 
 	if (index < 0) {
 		return _prop_materials[0];