private ZoneId getTimeZone(final XPathContext context, final String timeZone) {
        try {
            return DateFormatterCache.getZoneId(timeZone);
        } catch (final RuntimeException e) {
            final StringBuilder sb = new StringBuilder();
            sb.append("Time Zone '");
            sb.append(timeZone);
            sb.append("' is not recognised, defaulting to UTC");
            outputWarning(context, sb, e);
        }
        return ZoneOffset.UTC;
    }
Parsing dates that use week fields has to be done differently as week based parsing does not seem to
cope with conflicting default values for fields.
stroom-pipeline/src/main/java/stroom/pipeline/xsltfunctions/ParseDateTime.java