cocci: refactor common patterns to use xstrdup_or_null()

d64ea0f8 ("git-compat-util: add xstrdup_or_null helper",
2015-01-12) added a handy wrapper that allows us to get a duplicate
of a string or NULL if the original is NULL, but a handful of
codepath predate its introduction or just weren't aware of it.
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

contrib/coccinelle/xstrdup_or_null.cocci

+@@
+expression E;
+expression V;
+@@
+- if (E)
+-    V = xstrdup(E);
++ V = xstrdup_or_null(E);

git.c

@@ -35,8 +35,7 @@ static void save_env_before_alias(void)
 	orig_cwd = xgetcwd();
 	for (i = 0; i < ARRAY_SIZE(env_names); i++) {
 		orig_env[i] = getenv(env_names[i]);
-		if (orig_env[i])
-			orig_env[i] = xstrdup(orig_env[i]);
+		orig_env[i] = xstrdup_or_null(orig_env[i]);
 	}
 }
 

imap-send.c

@@ -1082,10 +1082,8 @@ static struct imap_store *imap_open_store(struct imap_server_conf *srvc, char *f
 			cred.protocol = xstrdup(srvc->use_ssl ? "imaps" : "imap");
 			cred.host = xstrdup(srvc->host);
 
-			if (srvc->user)
-				cred.username = xstrdup(srvc->user);
-			if (srvc->pass)
-				cred.password = xstrdup(srvc->pass);
+			cred.username = xstrdup_or_null(srvc->user);
+			cred.password = xstrdup_or_null(srvc->pass);
 
 			credential_fill(&cred);
 

mailmap.c

@@ -103,10 +103,8 @@ static void add_mapping(struct string_list *map,
 	} else {
 		struct mailmap_info *mi = xcalloc(1, sizeof(struct mailmap_info));
 		debug_mm("mailmap: adding (complex) entry for '%s'\n", old_email);
-		if (new_name)
-			mi->name = xstrdup(new_name);
-		if (new_email)
-			mi->email = xstrdup(new_email);
+		mi->name = xstrdup_or_null(new_name);
+		mi->email = xstrdup_or_null(new_email);
 		string_list_insert(&me->namemap, old_name)->util = mi;
 	}
 

refs.c

@@ -791,8 +791,7 @@ struct ref_update *ref_transaction_add_update(
 		hashcpy(update->new_sha1, new_sha1);
 	if (flags & REF_HAVE_OLD)
 		hashcpy(update->old_sha1, old_sha1);
-	if (msg)
-		update->msg = xstrdup(msg);
+	update->msg = xstrdup_or_null(msg);
 	return update;
 }
 

send-pack.c

@@ -181,8 +181,7 @@ static int receive_status(int in, struct ref *refs)
 			hint->status = REF_STATUS_REMOTE_REJECT;
 			ret = -1;
 		}
-		if (msg)
-			hint->remote_status = xstrdup(msg);
+		hint->remote_status = xstrdup_or_null(msg);
 		/* start our next search from the next ref */
 		hint = hint->next;
 	}

trailer.c

@@ -428,12 +428,9 @@ static int set_if_missing(struct conf_info *item, const char *value)
 static void duplicate_conf(struct conf_info *dst, struct conf_info *src)
 {
 	*dst = *src;
-	if (src->name)
-		dst->name = xstrdup(src->name);
-	if (src->key)
-		dst->key = xstrdup(src->key);
-	if (src->command)
-		dst->command = xstrdup(src->command);
+	dst->name = xstrdup_or_null(src->name);
+	dst->key = xstrdup_or_null(src->key);
+	dst->command = xstrdup_or_null(src->command);
 }
 
 static struct trailer_item *get_conf_item(const char *name)