Fix PR issues

Library/Homebrew/cli/args.rb

@@ -246,12 +246,11 @@ module Homebrew
         require "formula"
         require "missing_formula"
 
-        raise UsageError if name.empty?
+        raise UsageError if name.blank?
 
         rack = Formulary.to_rack(name.downcase)
 
         dirs = rack.directory? ? rack.subdirs : []
-
         raise NoSuchKegError, rack.basename if dirs.empty?
 
         linked_keg_ref = HOMEBREW_LINKED_KEGS/rack.basename
@@ -278,7 +277,7 @@ module Homebrew
             Keg.new(prefix)
           end
         rescue FormulaUnavailableError
-          raise <<~EOS
+          raise MultipleVersionsInstalledError, <<~EOS
             Multiple kegs installed to #{rack}
             However we don't know which one you refer to.
             Please delete (with rm -rf!) all but one and then try again.

Library/Homebrew/cmd/reinstall.rb

@@ -75,7 +75,7 @@ module Homebrew
 
     Homebrew.messages.display_messages
 
-    return if casks.empty?
+    return if casks.blank?
 
     reinstall_cmd = Cask::Cmd::Reinstall.new(casks)
     reinstall_cmd.verbose = args.verbose?

Library/Homebrew/cmd/uninstall.rb

@@ -123,7 +123,7 @@ module Homebrew
       end
     end
 
-    return if casks.empty?
+    return if casks.blank?
 
     cask_uninstall = Cask::Cmd::Uninstall.new(casks)
     cask_uninstall.force = args.force?