fix(hmp): prevent crash when passing anything non-existent to hmp funcs

ds.c

@@ -171,6 +171,10 @@ ds_hmp_t
 {
 	ds_hmp_t *hmp;
 
+	if (!data_len) {
+		return NULL;
+	}
+
 	hmp = calloc(1, sizeof(ds_hmp_t));
 	hmp->data_len = data_len;
 	hmp->data = calloc(data_len, sizeof(ds_sll_t **));
@@ -255,6 +259,10 @@ void
 	ds_sll_t *cur, *ll;
 	unsigned hash_pos;
 
+	if (!hmp || !key) {
+		return NULL;
+	}
+
 	hash_pos = _ds_hmp_gen_hash(key) % hmp->data_len;
 	ll = hmp->data[hash_pos];
 	if (!ll) {
@@ -279,6 +287,10 @@ void
 	ds_sll_t *ll, *cur;
 	_ds_hmp_kv_t *kv;
 
+	if (!hmp || !key) {
+		return NULL;
+	}
+
 	hash_pos = _ds_hmp_gen_hash(key) % hmp->data_len;
 	ll = hmp->data[hash_pos];
 	if (!ll) {