class ParameterMapValidator implements ConstraintValidator<ParameterMap, Map<String, ClientExpressionContainer>>,
        ValidationErrorDescriptorBuilder {

    @Override
    public boolean isValid(Map<String, ClientExpressionContainer> targetParameterMap, ConstraintValidatorContext context) {
        if (targetParameterMap != null) {
            for (String paramEl : targetParameterMap.keySet()) {
                if (paramEl == null
                    || paramEl.contains(".") // This check is explicitly defined because <dot> has special meaning in Data Engine and impl of ExpressionEvaluator
                    || NOT_A_TO_Z_OR_UNDERSCORE_PATTERN.matcher(paramEl.substring(0, 1)).matches()
                    || NOT_W_PATTERN.matcher(paramEl).find()) {
                    return false;
                }
            }
        }
        return true;
    }

}