private void isValidSystemID(String systemId) throws MappingException {
        if (StringUtils.isBlank(systemId)) {
            MappingUtils.throwMappingException("System ID is empty. Expected: " + VERSION_6_XSD
                                               + "'. Please see migration guide @ https://dozermapper.github.io/gitbook");
        }

        if (VERSION_5_XSD.equalsIgnoreCase(systemId)) {
            MappingUtils.throwMappingException("Dozer >= v6.0.0 uses a new XSD location. Your current config needs to be upgraded. "
                                               + "Found v5 XSD: '"
                                               + VERSION_5_XSD
                                               + "'. Expected v6 XSD: '"
                                               + VERSION_6_XSD
                                               + "'. Please see migration guide @ https://dozermapper.github.io/gitbook");
        }
    }
Resolves the schema specified in the mapping.xml.
Attempts to find locally on the classpath or by resolving the URL.
core/src/main/java/com/github/dozermapper/core/builder/xml/SchemaLSResourceResolver.java