[PATCH v2 29/42] merge: convert empty tree constant to the_hash_algo

To avoid dependency on a particular hash algorithm, convert a use of
EMPTY_TREE_SHA1_HEX to use the_hash_algo->empty_tree instead.  Since
both branches now use oid_to_hex, condense the if statement into a
ternary.

Signed-off-by: brian m. carlson <redacted>
---
 merge.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/merge.c b/merge.c
index f06a4773d4..5186cb6156 100644
--- a/merge.c
+++ b/merge.c

@@ -11,10 +11,7 @@
 
 static const char *merge_argument(struct commit *commit)
 {
-	if (commit)
-		return oid_to_hex(&commit->object.oid);
-	else
-		return EMPTY_TREE_SHA1_HEX;
+	return oid_to_hex(commit ? &commit->object.oid : the_hash_algo->empty_tree);
 }
 
 int index_has_changes(struct strbuf *sb)