Document that Net::IMAP#fetch will return nil instead of an emtpy array.

* lib/net/imap.rb (Net::IMAP#fetch): [DOC] Document that
  Net::IMAP#fetch will return nil instead of an emtpy array.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48207 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,8 @@
+Fri Oct 31 16:33:46 2014  Akinori MUSHA  <knu@iDaemons.org>
+
+	* lib/net/imap.rb (Net::IMAP#fetch): [DOC] Document that
+	  Net::IMAP#fetch will return nil instead of an emtpy array.
+
 Fri Oct 31 12:54:43 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* common.mk (.unicode-tables.time): needs Unicode files always,

lib/net/imap.rb

@@ -788,8 +788,10 @@ module Net
     # +attr+ is a list of attributes to fetch; see the documentation
     # for Net::IMAP::FetchData for a list of valid attributes.
     #
-    # The return value is an array of Net::IMAP::FetchData. For
-    # example:
+    # The return value is an array of Net::IMAP::FetchData or nil
+    # (instead of an empty array) if there is no matching message.
+    #
+    # For example:
     #
     #   p imap.fetch(6..8, "UID")
     #   #=> [#<Net::IMAP::FetchData seqno=6, attr={"UID"=>98}>, \\