From dd6ef6ff029003c7be0aa393108d13a077051cdb Mon Sep 17 00:00:00 2001
From: Tom Finegan <tomfinegan@google.com>
Date: Tue, 1 Dec 2020 14:37:24 -0800
Subject: [PATCH] draco: Fix empty list handling in older CMakes.

Older CMake releases don't support empty list variables with list(FILTER).
---
 cmake/draco_targets.cmake | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/cmake/draco_targets.cmake b/cmake/draco_targets.cmake
index ffe1f7d..a914f51 100644
--- a/cmake/draco_targets.cmake
+++ b/cmake/draco_targets.cmake
@@ -331,8 +331,13 @@ macro(draco_add_library)
   endif()
 
   # Determine if $lib_NAME is a header only target.
-  set(sources_list ${lib_SOURCES})
-  list(FILTER sources_list INCLUDE REGEX cc$)
+  unset(sources_list)
+
+  if(lib_SOURCES)
+    set(sources_list ${lib_SOURCES})
+    list(FILTER sources_list INCLUDE REGEX cc$)
+  endif()
+
   if(NOT sources_list)
     if(NOT XCODE)
       # This is a header only target. Tell CMake the link language.