diff --git a/src/api/api_context.cpp b/src/api/api_context.cpp
index 47a25f313..bc48874a7 100644
--- a/src/api/api_context.cpp
+++ b/src/api/api_context.cpp
@@ -131,7 +131,7 @@ namespace api {
     }
 
     char * context::mk_external_string(char const * str) {
-        m_string_buffer = str;
+        m_string_buffer = str?str:"";
         return const_cast<char *>(m_string_buffer.c_str());
     }