private ExpressionOperator createExpression(final Op op, final String feedName) {
        final ExpressionOperator.Builder builder = ExpressionOperator.builder().op(op);
        builder.addTextTerm(FEED, Condition.EQUALS, feedName);
        return builder.build();
    }
This ought to behave in a consistent way with CommonExpressionMapper
stroom-search/stroom-expression-matcher/src/test/java/stroom/expression/matcher/TestExpressionMatcher.java