Merge branch 'jk/blame-commit-label' into maint

"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

git-compat-util.h

@@ -678,6 +678,11 @@ extern char *xgetcwd(void);
 
 #define REALLOC_ARRAY(x, alloc) (x) = xrealloc((x), (alloc) * sizeof(*(x)))
 
+static inline char *xstrdup_or_null(const char *str)
+{
+	return str ? xstrdup(str) : NULL;
+}
+
 static inline size_t xsize_t(off_t len)
 {
 	if (len > (size_t) len)