Tweak the nil encoding logic

I must've managed to miss the PR update from Stanislav the other day
when merging this.

c_src/encoder.c

@@ -713,11 +713,15 @@ encode_iter(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
             stack = enif_make_list_cell(env, e->atoms->ref_array, stack);
             stack = enif_make_list_cell(env, item, stack);
         } else if(enif_compare(curr, e->atoms->atom_null) == 0 
-                    || (e->use_nil && enif_compare(curr, e->atoms->atom_nil) == 0)) {
             if(!enc_literal(e, "null", 4)) {
                 ret = enc_error(e, "null");
                 goto done;
-            }        
+            }
+        } else if(e->use_nil && enif_compare(curr, e->atoms->atom_nil) == 0)) {
+            if(!enc_literal(e, "null", 4)) {
+                ret = enc_error(e, "null");
+                goto done;
+            }
         } else if(enif_compare(curr, e->atoms->atom_true) == 0) {
             if(!enc_literal(e, "true", 4)) {
                 ret = enc_error(e, "true");