t2107: abstract away SHA-1-specific constants

Use the $EMPTY_BLOB variable instead of hard-coding a hash.

Signed-off-by: brian m. carlson <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: bk2204

t/t2107-update-index-basic.sh

@@ -85,9 +85,9 @@ test_expect_success '--chmod=+x and chmod=-x in the same argument list' '
 	>B &&
 	git add A B &&
 	git update-index --chmod=+x A --chmod=-x B &&
-	cat >expect <<-\EOF &&
-	100755 e69de29bb2d1d6434b8b29ae775ad8c2e48c5391 0	A
-	100644 e69de29bb2d1d6434b8b29ae775ad8c2e48c5391 0	B
+	cat >expect <<-EOF &&
+	100755 $EMPTY_BLOB 0	A
+	100644 $EMPTY_BLOB 0	B
 	EOF
 	git ls-files --stage A B >actual &&
 	test_cmp expect actual