Fix audit when tap is nil

This is the case when a formula is passed as a filename.

1 files changed, 2 insertions, 2 deletions

diff --git a/Library/Homebrew/cmd/audit.rb b/Library/Homebrew/cmd/audit.rb
index a583f3bbf..4851c0744 100644
--- a/Library/Homebrew/cmd/audit.rb
+++ b/Library/Homebrew/cmd/audit.rb
@@ -420,11 +420,11 @@ class FormulaAuditor
   end
 
   def audit_specs
-    if head_only?(formula) && formula.tap.downcase != "homebrew/homebrew-head-only"
+    if head_only?(formula) && formula.tap.to_s.downcase != "homebrew/homebrew-head-only"
       problem "Head-only (no stable download)"
     end
 
-    if devel_only?(formula) && formula.tap.downcase != "homebrew/homebrew-devel-only"
+    if devel_only?(formula) && formula.tap.to_s.downcase != "homebrew/homebrew-devel-only"
       problem "Devel-only (no stable download)"
     end