SymbolStringSearchPolicy was necessary in earlier versions of Dolphin since (as per the class comment) "Normally Symbols are not considered equal to Strings even when they contain the same characters."
The class is no longer required (hence its removal) since Strings and Symbols with the same sequence of Characters now compare equal:
#abc = 'abc' "false"
#abs = 'abc' "true"
You should now be able to use EqualitySearchPolicy instead with the same results.
Hope this helps,