diff --git a/Library/Homebrew/cmd/link.rb b/Library/Homebrew/cmd/link.rb
index 23440f1c35..9c43e48e96 100644
--- a/Library/Homebrew/cmd/link.rb
+++ b/Library/Homebrew/cmd/link.rb
@@ -45,6 +45,8 @@ module Homebrew
               To install, run:
                 brew install --HEAD #{name}
             EOS
+
+            nil
           end
         else
           args.named.to_latest_kegs
diff --git a/Library/Homebrew/dev-cmd/bump-unversioned-casks.rb b/Library/Homebrew/dev-cmd/bump-unversioned-casks.rb
index b12508657f..4d5bcdbbd9 100644
--- a/Library/Homebrew/dev-cmd/bump-unversioned-casks.rb
+++ b/Library/Homebrew/dev-cmd/bump-unversioned-casks.rb
@@ -125,6 +125,8 @@ module Homebrew
             end
           rescue => e
             onoe e
+
+            nil
           end
 
           if sha256.present? && last_sha256 != sha256
@@ -134,6 +136,8 @@ module Homebrew
               end
             rescue Timeout::Error
               onoe "Timed out guessing version for cask '#{cask}'."
+
+              nil
             end
 
             if version
diff --git a/Library/Homebrew/extend/kernel.rb b/Library/Homebrew/extend/kernel.rb
index 40e489cf8f..6058dbe5f1 100644
--- a/Library/Homebrew/extend/kernel.rb
+++ b/Library/Homebrew/extend/kernel.rb
@@ -61,26 +61,29 @@ module Kernel
   # Print a warning message.
   #
   # @api public
+  sig { params(message: T.any(String, Exception)).void }
   def opoo(message)
     Tty.with($stderr) do |stderr|
       stderr.puts Formatter.warning(message, label: "Warning")
-      GitHub::Actions.puts_annotation_if_env_set(:warning, message)
+      GitHub::Actions.puts_annotation_if_env_set(:warning, message.to_s)
     end
   end
 
   # Print an error message.
   #
   # @api public
+  sig { params(message: T.any(String, Exception)).void }
   def onoe(message)
     Tty.with($stderr) do |stderr|
       stderr.puts Formatter.error(message, label: "Error")
-      GitHub::Actions.puts_annotation_if_env_set(:error, message)
+      GitHub::Actions.puts_annotation_if_env_set(:error, message.to_s)
     end
   end
 
   # Print an error message and fail at the end of the program.
   #
   # @api public
+  sig { params(error: T.any(String, Exception)).void }
   def ofail(error)
     onoe error
     Homebrew.failed = true