public Set<String> getRequiredPropertyNames() {
        return Collections.unmodifiableSet(this.requiredPropertyNames);
    }
Retrieve the names (as to be included in the schema definition) of all required properties (in undefined order).

@return names of required properties
jsonschema-generator/src/main/java/com/github/victools/jsonschema/generator/impl/MemberCollectionContextImpl.java