Accept `sleep(nil)` as sleep forever. (#7484)

process.c

@@ -4918,6 +4918,9 @@ rb_f_spawn(int argc, VALUE *argv, VALUE _)
  *  thread calls Thread#run. Called without an argument, sleep()
  *  will sleep forever.
  *
+ *  If the +duration+ is not supplied, or is +nil+, the thread sleeps forever.
+ *  Threads in this state may still be interrupted by other threads.
+ *
  *     Time.new    #=> 2008-03-08 19:56:19 +0900
  *     sleep 1.2   #=> 1
  *     Time.new    #=> 2008-03-08 19:56:20 +0900
@@ -4935,7 +4938,7 @@ rb_f_sleep(int argc, VALUE *argv, VALUE _)
         rb_fiber_scheduler_kernel_sleepv(scheduler, argc, argv);
     }
     else {
-        if (argc == 0) {
+        if (argc == 0 || (argc == 1 && NIL_P(argv[0]))) {
             rb_thread_sleep_forever();
         }
         else {

spec/ruby/core/kernel/sleep_spec.rb

@@ -33,10 +33,6 @@ describe "Kernel#sleep" do
     -> { sleep(-1) }.should raise_error(ArgumentError)
   end
 
-  it "raises a TypeError when passed nil" do
-    -> { sleep(nil)   }.should raise_error(TypeError)
-  end
-
   it "raises a TypeError when passed a String" do
     -> { sleep('2')   }.should raise_error(TypeError)
   end
@@ -55,6 +51,29 @@ describe "Kernel#sleep" do
     t.wakeup
     t.value.should == 5
   end
+
+  ruby_version_is ""..."3.3" do
+    it "raises a TypeError when passed nil" do
+      -> { sleep(nil)   }.should raise_error(TypeError)
+    end
+  end
+
+  ruby_version_is "3.3" do
+    it "accepts a nil duration" do
+      running = false
+      t = Thread.new do
+        running = true
+        sleep(nil)
+        5
+      end
+
+      Thread.pass until running
+      Thread.pass while t.status and t.status != "sleep"
+
+      t.wakeup
+      t.value.should == 5
+    end
+  end
 end
 
 describe "Kernel.sleep" do