public String getIdentifier() {
        return identifier;
    }
Returns the unique identifier assigned to this record, if any. If this
record is not uniquely identifiable, this may be null.

@return
    The unique identifier assigned to this record, or null if this
    record has no such identifier.
guacamole/src/main/java/org/apache/guacamole/rest/history/APIActivityRecord.java