update nip-02 to disallow `null`, only allow strings in tags.

fixes https://github.com/nostr-protocol/nips/pull/15
fixes https://github.com/fiatjaf/nostr-army-knife/issues/2
fixes https://github.com/fiatjaf/relayer/issues/3

1 files changed, 1 insertions, 1 deletions

diff --git a/01.md b/01.md
index 8bf7fc3..3fd1cdc 100644
--- a/01.md
+++ b/01.md
@@ -38,7 +38,7 @@ To obtain the `event.id`, we `sha256` the serialized event. The serialization is
   <pubkey, as a (lowercase) hex string>,
   <created_at, as a number>,
   <kind, as a number>,
-  <tags, as an array of arrays of strings>,
+  <tags, as an array of arrays of non-null strings>,
   <content, as a string>
 ]
 ```