Don’t crash when writing to null hash elem

It’s possible for XS code to create hash entries with null values.
pp_helem and pp_slice were not taking that into account.  In fact,
the core produces such hash entries, but they are rarely visible from
Perl.  It’s good to check for them anyway.

1 files changed, 13 insertions, 0 deletions

diff --git a/ext/XS-APItest/t/hash.t b/ext/XS-APItest/t/hash.t
index f66edfa1f5..06983c570d 100644
--- a/ext/XS-APItest/t/hash.t
+++ b/ext/XS-APItest/t/hash.t
@@ -245,6 +245,19 @@ sub test_precomputed_hashes {
       'newHVhv on tied hash';
 }
 
+# helem on entry with null value
+# This is actually a test for a Perl operator, not an XS API test.  But it
+# requires a hash that can only be produced by XS (although recently it
+# could be encountered when tying hint hashes).
+{
+    my %h;
+    fill_hash_with_nulls(\%h);
+    eval{ $h{84} = 1 };
+    pass 'no crash when writing to hash elem with null value';
+    eval{ @h{85} = 1 };
+    pass 'no crash when writing to hash elem with null value via slice';
+}
+
 done_testing;
 exit;