DEV: prevents attemps to redefine THEME_TARGETS constant (#8121)

DEV: prevents attemps to redefine THEME_TARGETS constant (#8121)

diff --git a/lib/stylesheet/importer.rb b/lib/stylesheet/importer.rb
index 5cf12e0..a0fccd0 100644
--- a/lib/stylesheet/importer.rb
+++ b/lib/stylesheet/importer.rb
@@ -7,7 +7,7 @@ module Stylesheet
   class Importer < SassC::Importer
     include GlobalPath
 
-    THEME_TARGETS = %w{embedded_theme mobile_theme desktop_theme}
+    THEME_TARGETS ||= %w{embedded_theme mobile_theme desktop_theme}
 
     def self.special_imports
       @special_imports ||= {}

GitHub sha: e5af03be