use xstrdup_or_null to replace ternary conditionals

This replaces "x ? xstrdup(x) : NULL" with xstrdup_or_null(x).
The change is fairly mechanical, with the exception of
resolve_refdup, which can eliminate a temporary variable.

There are still a few hits grepping for "?.*xstrdup", but
these are of slightly different forms and cannot be
converted (e.g., "x ? xstrdup(x->foo) : NULL").
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

config.c

@@ -1329,7 +1329,7 @@ static int configset_add_value(struct config_set *cs, const char *key, const cha
 		string_list_init(&e->value_list, 1);
 		hashmap_add(&cs->config_hash, e);
 	}
-	si = string_list_append_nodup(&e->value_list, value ? xstrdup(value) : NULL);
+	si = string_list_append_nodup(&e->value_list, xstrdup_or_null(value));
 
 	ALLOC_GROW(cs->list.items, cs->list.nr + 1, cs->list.alloc);
 	l_item = &cs->list.items[cs->list.nr++];

grep.c

@@ -1646,8 +1646,8 @@ void grep_source_init(struct grep_source *gs, enum grep_source_type type,
 		      const void *identifier)
 {
 	gs->type = type;
-	gs->name = name ? xstrdup(name) : NULL;
-	gs->path = path ? xstrdup(path) : NULL;
+	gs->name = xstrdup_or_null(name);
+	gs->path = xstrdup_or_null(path);
 	gs->buf = NULL;
 	gs->size = 0;
 	gs->driver = NULL;

notes.c

@@ -1006,7 +1006,7 @@ void init_notes(struct notes_tree *t, const char *notes_ref,
 	t->root = (struct int_node *) xcalloc(1, sizeof(struct int_node));
 	t->first_non_note = NULL;
 	t->prev_non_note = NULL;
-	t->ref = notes_ref ? xstrdup(notes_ref) : NULL;
+	t->ref = xstrdup_or_null(notes_ref);
 	t->combine_notes = combine_notes;
 	t->initialized = 1;
 	t->dirty = 0;

refs.c

@@ -1529,8 +1529,7 @@ const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int rea
 
 char *resolve_refdup(const char *ref, unsigned char *sha1, int reading, int *flag)
 {
-	const char *ret = resolve_ref_unsafe(ref, sha1, reading, flag);
-	return ret ? xstrdup(ret) : NULL;
+	return xstrdup_or_null(resolve_ref_unsafe(ref, sha1, reading, flag));
 }
 
 /* The argument to filter_refs */

remote.c

@@ -975,8 +975,8 @@ struct ref *copy_ref(const struct ref *ref)
 	cpy = xmalloc(sizeof(struct ref) + len + 1);
 	memcpy(cpy, ref, sizeof(struct ref) + len + 1);
 	cpy->next = NULL;
-	cpy->symref = ref->symref ? xstrdup(ref->symref) : NULL;
-	cpy->remote_status = ref->remote_status ? xstrdup(ref->remote_status) : NULL;
+	cpy->symref = xstrdup_or_null(ref->symref);
+	cpy->remote_status = xstrdup_or_null(ref->remote_status);
 	cpy->peer_ref = copy_ref(ref->peer_ref);
 	return cpy;
 }

shallow.c

@@ -21,7 +21,7 @@ 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)

walker.c

@@ -232,7 +232,7 @@ int walker_targets_stdin(char ***target, const char ***write_ref)
 			REALLOC_ARRAY(*write_ref, targets_alloc);
 		}
 		(*target)[targets] = xstrdup(tg_one);
-		(*write_ref)[targets] = rf_one ? xstrdup(rf_one) : NULL;
+		(*write_ref)[targets] = xstrdup_or_null(rf_one);
 		targets++;
 	}
 	strbuf_release(&buf);