Add. Support set null as array in multi API

src/lcmulti.c

@@ -424,11 +424,17 @@ static int lcurl_opt_set_string_array_(lua_State *L, int opt){
   lcurl_multi_t *p = lcurl_getmulti(L);
   CURLMcode code;
   int n;
+
+  if (lutil_is_null(L, 2)) {
+    n = 0;
+  }
+  else {
     luaL_argcheck(L, lua_type(L, 2) == LUA_TTABLE, 2, "array expected");
     n = lua_rawlen(L, 2);
+  }
+
   if(n == 0){
-    char *val[] = {NULL};
-    code = curl_multi_setopt(p->curl, opt, val);
+    code = curl_multi_setopt(p->curl, opt, 0);
   }
   else{
     int i;

test/test_easy.lua

@@ -1064,11 +1064,12 @@ end
 
 local _ENV = TEST_CASE'set_null'             if ENABLE then
 
-local c
+local c, m
 
 function teardown()
   if c then c:close() end
-  c = nil
+  if m then m:close() end
+  m, c = nil
 end
 
 function test_string()
@@ -1109,6 +1110,14 @@ function test_slist_via_table()
   assert_not_match("X%-Custom:%s*value\r\n", headers)
 end
 
+function test_multi_set_array()
+  m = curl.multi()
+  m:setopt_pipelining_site_bl{
+    '127.0.0.1'
+  }
+  assert_equal(m, m:setopt_pipelining_site_bl(null))
+end
+
 end
 
 RUN()