diff --git a/src/klotski_core/CMakeLists.txt b/src/klotski_core/CMakeLists.txt
index 56adcb1..269c95d 100644
--- a/src/klotski_core/CMakeLists.txt
+++ b/src/klotski_core/CMakeLists.txt
@@ -51,13 +51,23 @@ endmacro()
 
 ################################################################################
 
-set(GIT_BRANCH "")
 set(GIT_TAG_LONG "")
-set(GIT_COMMIT_LONG "")
-
 git_tag(GIT_TAG_LONG)
+if(GIT_TAG_LONG STREQUAL "")  # without git tag
+    set(GIT_TAG_LONG "unknown")
+endif()
+
+set(GIT_BRANCH "")
 git_branch(GIT_BRANCH)
+if(GIT_BRANCH STREQUAL "")  # without git branch
+    set(GIT_BRANCH "unknown")
+endif()
+
+set(GIT_COMMIT_LONG "")
 git_commit_id(GIT_COMMIT_LONG)
+if(GIT_COMMIT_LONG STREQUAL "")  # without git commit
+    set(GIT_COMMIT_LONG "unknown")
+endif()
 
 set(PLAT "${CMAKE_SYSTEM_NAME}")
 set(ARCH "${CMAKE_SYSTEM_PROCESSOR}")
diff --git a/test/ffi/metadata.cc b/test/ffi/metadata.cc
index 346123b..b241559 100644
--- a/test/ffi/metadata.cc
+++ b/test/ffi/metadata.cc
@@ -3,6 +3,16 @@
 #include "gtest/gtest.h"
 
 TEST(FFI, metadata) {
+    EXPECT_STRNE(get_author(), "");
+    EXPECT_STRNE(get_git_tag(), "");
+    EXPECT_STRNE(get_version(), "");
+    EXPECT_STRNE(get_commit_id(), "");
+    EXPECT_STRNE(get_build_time(), "");
+    EXPECT_STRNE(get_git_branch(), "");
+    EXPECT_STRNE(get_project_url(), "");
+    EXPECT_STRNE(get_system_info(), "");
+    EXPECT_STRNE(get_compiler_info(), "");
+
     EXPECT_STREQ(get_author(), AUTHOR);
     EXPECT_STREQ(get_git_tag(), GIT_TAG_ID);
     EXPECT_STREQ(get_version(), VERSION_STR);