Merge branch 'jk/blame-commit-label'

"git blame HEAD -- missing" failed to correctly say "HEAD" when it
tried to say "No such path 'missing' in HEAD".

* jk/blame-commit-label:
  blame.c: fix garbled error message
  use xstrdup_or_null to replace ternary conditionals
  builtin/commit.c: use xstrdup_or_null instead of envdup
  builtin/apply.c: use xstrdup_or_null instead of null_strdup
  git-compat-util: add xstrdup_or_null helper

shallow.c

@@ -22,7 +22,7 @@ void set_alternate_shallow_file(const char *path, int override)
 	if (alternate_shallow_file && !override)
 		return;
 	free(alternate_shallow_file);
-	alternate_shallow_file = path ? xstrdup(path) : NULL;
+	alternate_shallow_file = xstrdup_or_null(path);
 }
 
 int register_shallow(const unsigned char *sha1)