src/main/java/org/xmlet/xsdparser/xsdelements/AttributeValidations.java
public static Integer validateRequiredNonNegativeInteger(String elementName, String attributeName, String value){
        if (value == null) throw new ParsingException(attributeMissingMessage(elementName, attributeName));

        return validateNonNegativeInteger(elementName, attributeName, value);
    }
public static Integer validateRequiredNonNegativeInteger(String elementName, String attributeName, String value){
        if (value == null) throw new ParsingException(attributeMissingMessage(elementName, attributeName));

        return validateNonNegativeInteger(elementName, attributeName, value);
    }
Validates if a given String is a non negative {@link Integer}. Throws an exception if the {@link String} isn't a
non negative {@link Integer}.
@param elementName The element name containing the field with the {@link Integer} value.
@param attributeName The name of the attribute with the {@link Integer}.
@param value The value to be parsed to a {@link Integer} object.
@return The parsed {@link Integer} value.