Update #20737 to address feedback

Given that this pull request affects a mutable value, we need to test
for and document the affects on the receiver in this case.

Additionally, this pull request was missing a CHANGELOG entry.

1 files changed, 5 insertions, 2 deletions

diff --git a/activesupport/lib/active_support/multibyte/chars.rb b/activesupport/lib/active_support/multibyte/chars.rb
index a76692ec4b..707cf200b5 100644
--- a/activesupport/lib/active_support/multibyte/chars.rb
+++ b/activesupport/lib/active_support/multibyte/chars.rb
@@ -86,7 +86,8 @@ module ActiveSupport #:nodoc:
       end
 
       # Works like <tt>String#slice!</tt>, but returns an instance of
-      # Chars, or nil if the string was not modified.
+      # Chars, or nil if the string was not modified. The string will not be
+      # modified if the range given is out of bounds
       #
       #   string = 'Welcome'
       #   string.mb_chars.slice!(3)    # => #<ActiveSupport::Multibyte::Chars:0x000000038109b8 @wrapped_string="c">
@@ -95,7 +96,9 @@ module ActiveSupport #:nodoc:
       #   string # => 'me'
       def slice!(*args)
         string_sliced = @wrapped_string.slice!(*args)
-        string_sliced ? chars(string_sliced) : nil
+        if string_sliced
+          chars(string_sliced)
+        end
       end
 
       # Reverses all characters in the string.