feat: add Oid::is_null() - previously it was only available on ObjectId.

Author: Byron

gix-hash/src/oid.rs

@@ -1,6 +1,6 @@
 use std::{convert::TryInto, fmt, hash};
 
-use crate::{ObjectId, SIZE_OF_SHA1_DIGEST};
+use crate::{Kind, ObjectId, SIZE_OF_SHA1_DIGEST};
 
 /// A borrowed reference to a hash identifying objects.
 ///
@@ -137,6 +137,15 @@ impl oid {
             hex_len: self.bytes.len() * 2,
         }
     }
+
+    /// Returns `true` if this hash consists of all null bytes.
+    #[inline]
+    #[doc(alias = "is_zero", alias = "git2")]
+    pub fn is_null(&self) -> bool {
+        match self.kind() {
+            Kind::Sha1 => &self.bytes == oid::null_sha1().as_bytes(),
+        }
+    }
 }
 
 /// Sha1 specific methods

gix-hash/tests/oid/mod.rs

@@ -13,3 +13,9 @@ mod to_hex_with_len {
         );
     }
 }
+
+#[test]
+fn is_null() {
+    assert!(gix_hash::Kind::Sha1.null().is_null());
+    assert!(gix_hash::Kind::Sha1.null().as_ref().is_null());
+}