Declare `RHASH_AR_TABLE` and `RHASH_ST_TABLE` return non-null

hash.c

@@ -725,7 +725,8 @@ ar_force_convert_table(VALUE hash, const char *file, int line)
         return RHASH_ST_TABLE(hash);
     }
 
-    if (RHASH_AR_TABLE(hash)) {
+    RUBY_ASSERT(RHASH_AR_TABLE(hash));
+    {
         unsigned i, bound = RHASH_AR_TABLE_BOUND(hash);
 
         rb_st_init_existing_table_with_size(new_tab, &objhash, RHASH_AR_TABLE_SIZE(hash));
@@ -738,9 +739,6 @@ ar_force_convert_table(VALUE hash, const char *file, int line)
         }
         ar_free_and_clear_table(hash);
     }
-    else {
-        rb_st_init_existing_table_with_size(new_tab, &objhash, 0);
-    }
 
     RHASH_ST_TABLE_SET(hash, new_tab);
 

internal/hash.h

@@ -124,12 +124,14 @@ RHASH_AR_TABLE_P(VALUE h)
     return ! FL_TEST_RAW(h, RHASH_ST_TABLE_FLAG);
 }
 
+RBIMPL_ATTR_RETURNS_NONNULL()
 static inline struct ar_table_struct *
 RHASH_AR_TABLE(VALUE h)
 {
     return (struct ar_table_struct *)((uintptr_t)h + sizeof(struct RHash));
 }
 
+RBIMPL_ATTR_RETURNS_NONNULL()
 static inline st_table *
 RHASH_ST_TABLE(VALUE h)
 {