allow empty curly-braces in defval

Author: HoneyryderChuck

lib/netsnmp/mib/parser.rb

@@ -476,7 +476,7 @@ def with_separator(atom, separator = nil)
     end
 
     rule(:valueof_simple_syntax) do
-      value | lowercase_identifier | text | curly(object_identifiers_defval)
+      value | lowercase_identifier | text | curly(object_identifiers_defval.maybe)
     end
 
     rule(:object_identifiers_defval) do