PatientEventListener.java

        @Override
        public String getExternalId()
        {
            try {
                for (Object identifierUncast : this.getData("identifiers")) {
                    Map.Entry<String, String> identifier = (Map.Entry<String, String>) identifierUncast;
                    if (identifier.getKey().equalsIgnoreCase("external_id")){
                        return identifier.getValue();
                    }
                }
            } catch (Exception ex) {
                return null;
            }
            return null;
        }

Do it (almost) like this.

for (ImmutablePair<String, String> identifier : this.<ImmutablePair<String, String>>getData("identifiers")) {