Don't throw an exception on empty string io on JRuby. Fix #883.

lib/nokogiri/xml/document.rb

@@ -45,12 +45,13 @@ def self.parse string_or_io, url = nil, encoding = nil, options = ParseOptions::
         # Give the options to the user
         yield options if block_given?
 
+        return new if empty_doc?(string_or_io)
+
         doc = if string_or_io.respond_to?(:read)
           url ||= string_or_io.respond_to?(:path) ? string_or_io.path : nil
           read_io(string_or_io, url, encoding, options.to_i)
         else
           # read_memory pukes on empty docs
-          return new if string_or_io.nil? or string_or_io.empty?
           read_memory(string_or_io, url, encoding, options.to_i)
         end
 
@@ -260,6 +261,12 @@ def to_java
       end
 
       private
+      def self.empty_doc? string_or_io
+        string_or_io.nil? ||
+          (string_or_io.respond_to?(:empty?) && string_or_io.empty?) ||
+          (string_or_io.respond_to?(:eof?) && string_or_io.eof?)
+      end
+
       def implied_xpath_context
         "/"
       end

test/xml/test_document.rb

@@ -580,6 +580,11 @@ def test_parse_can_take_io
         assert set.length > 0
       end
 
+      def test_parsing_empty_io
+        doc = Nokogiri::XML.parse(StringIO.new(''))
+        refute_nil doc
+      end
+
       def test_search_on_empty_documents
         doc = Nokogiri::XML::Document.new
         ns = doc.search('//foo')