Need to check if merging hash is empty; fix
MODIFY
src/hash.c
src/hash.c
@@ -969,6 +969,7 @@ mrb_hash_merge(mrb_state *mrb, mrb_value hash1, mrb_value hash2)
h1 = RHASH_TBL(hash1);
h2 = RHASH_TBL(hash2);
+ if (!h2) return;
if (!h1) {
RHASH_TBL(hash1) = kh_copy(ht, mrb, h2);
return;

Need to check if merging hash is empty; fix #4107