private void updateAttribute(final FsTarget target, final QueryField key, final String value) {
        if (!target.getAttributes().containsKey(key.getFldName())) {
            target.getAttributes().put(key.getFldName(), value);
        }
    }
Creates a new file system stream target.

@return A new file system target.
stroom-data/stroom-data-store-impl-fs/src/main/java/stroom/data/store/impl/fs/FsTarget.java