[ruby/reline] Change Reline.add_dialog_proc(name, nil) to properly

remove dialog_proc
(https://github.com/ruby/reline/pull/532)

https://github.com/ruby/reline/commit/43283b2f37

lib/reline.rb

@@ -166,9 +166,13 @@ module Reline
 
     DialogProc = Struct.new(:dialog_proc, :context)
     def add_dialog_proc(name_sym, p, context = nil)
-      raise ArgumentError unless p.respond_to?(:call) or p.nil?
       raise ArgumentError unless name_sym.instance_of?(Symbol)
-      @dialog_proc_list[name_sym] = DialogProc.new(p, context)
+      if p.nil?
+        @dialog_proc_list.delete(name_sym)
+      else
+        raise ArgumentError unless p.respond_to?(:call)
+        @dialog_proc_list[name_sym] = DialogProc.new(p, context)
+      end
     end
 
     def dialog_proc(name_sym)

test/reline/test_reline.rb

@@ -321,6 +321,9 @@ class Reline::Test < Reline::TestCase
     d = Reline.dialog_proc(:test_proc)
     assert_equal(dummy_proc_2, d.dialog_proc)
 
+    Reline.add_dialog_proc(:test_proc, nil)
+    assert_nil(Reline.dialog_proc(:test_proc))
+
     l = lambda {}
     Reline.add_dialog_proc(:test_lambda, l)
     d = Reline.dialog_proc(:test_lambda)