fix enum default logic for bools that default to false

lib/msf/core/opt_base.rb

@@ -36,7 +36,11 @@ module Msf
         self.required = required
         self.desc     = attrs.is_a?(String) ? attrs : desc
         self.enums    = [ *(enums) ].map { |x| x.to_s }
-        self.default  = default || enums[0]
+        if default.nil? && enums.length > 0
+          self.default  = enums[0]
+        else
+          self.default = default
+        end
         regex_temp    = regex
       else
         self.required = attrs[0] || required

lib/msf/core/opt_enum.rb

@@ -25,7 +25,11 @@ module Msf
     end
 
     def normalize(value = self.value)
-      !valid?(value) ? nil : value.to_s
+      if valid?(value)
+        value.to_s
+      else
+        nil
+      end
     end
 
     def desc=(value)