private Stream<String> tokenizeExpression(final String expression) {
        if (expression != null) {
            return Arrays.stream(expression.split(DELIMITER))
                    .map(String::trim)
                    .filter(token -> !token.isEmpty());
        } else {
            return Stream.empty();
        }
    }
Split an expression into is component terms. Useful for extracting terms for use with "in" or "contains"
conditions

@param expression - Example: "1,2, 3"
@return - Stream of terms. Example: [ "1", "2", "3" ]
stroom-search/stroom-search-elastic/src/main/java/stroom/search/elastic/search/SearchExpressionQueryBuilder.java