merge revision(s) 0b2613f44309bddae45562c9f3a14ed43e56959b: [Backport #19640]

	`rb_io_puts` should not write zero length strings. (#7806)

	---
	 io.c                  | 40 ++++++++++++++++++++++++----------------
	 test/fiber/test_io.rb | 28 ++++++++++++++++++++++++++++
	 2 files changed, 52 insertions(+), 16 deletions(-)

1 files changed, 28 insertions, 0 deletions

diff --git a/test/fiber/test_io.rb b/test/fiber/test_io.rb
index de88745e57..c1ad56a8cf 100644
--- a/test/fiber/test_io.rb
+++ b/test/fiber/test_io.rb
@@ -170,6 +170,34 @@ class TestFiberIO < Test::Unit::TestCase
     assert_predicate(o, :closed?)
   end
 
+  def test_puts_empty
+    omit "UNIXSocket is not defined!" unless defined?(UNIXSocket)
+
+    i, o = UNIXSocket.pair
+    i.nonblock = false
+    o.nonblock = false
+
+    thread = Thread.new do
+      # This scheduler provides non-blocking `io_read`/`io_write`:
+      scheduler = IOBufferScheduler.new
+      Fiber.set_scheduler scheduler
+
+      Fiber.schedule do
+        # This was causing a segfault on older Ruby.
+        o.puts ""
+        o.puts nil
+        o.close
+      end
+    end
+
+    thread.join
+
+    message = i.read
+    i.close
+
+    assert_equal $/*2, message
+  end
+
   def test_io_select
     omit "UNIXSocket is not defined!" unless defined?(UNIXSocket)