public Set<ByteString> keys(ByteString namespace){
  if (namespace != null) {
    SetMultimap<ByteString,ByteString> namespaceData=contents.get(namespace);
    if (namespaceData != null) {
      return namespaceData.keySet();
    }
  }
  return Collections.emptySet();
}

public Set < ByteString > keys ( ByteString namespace ) { if ( namespace != null ) { SetMultimap < ByteString , ByteString > namespaceData = contents . get ( namespace ) ; if ( namespaceData != null ) { return namespaceData . keySet ( ) ; } } return Collections . emptySet ( ) ; }
returns a set view of the keys in the specified namespace that have 1 or more values assigned
