NullPointerException in archetype validation when value set doesn't have an id

[J3173]

When validating an archetype which has a value set without an id, the validation process fails with a NullPointerException.

Raises NullPointerException:

    value_sets = <
        ["ac9004"] = <
            members = <"at8", "at9", "at10", "at11", "at13">
        >
    >

Works:

    value_sets = <
        ["ac9004"] = <
            id = <"ac9004">
            members = <"at8", "at9", "at10", "at11", "at13">
        >
    >

Stack trace:

java.lang.NullPointerException: Cannot invoke "String.startsWith(String)" because "code" is null
	at com.nedap.archie.aom.utils.AOMUtils.isValueSetCode(AOMUtils.java:45)
	at com.nedap.archie.aom.terminology.ArchetypeTerminology.hasValueSetCode(ArchetypeTerminology.java:215)
	at com.nedap.archie.archetypevalidator.validations.BasicTerminologyValidation.validateValueSets(BasicTerminologyValidation.java:105)
	at com.nedap.archie.archetypevalidator.validations.BasicTerminologyValidation.validate(BasicTerminologyValidation.java:31)
	at com.nedap.archie.archetypevalidator.ArchetypeValidationBase.validate(ArchetypeValidationBase.java:35)
	at com.nedap.archie.archetypevalidator.ArchetypeValidator.runValidations(ArchetypeValidator.java:247)
	at com.nedap.archie.archetypevalidator.ArchetypeValidator.validate(ArchetypeValidator.java:187)