in nbm-maven-plugin/src/main/java/org/apache/netbeans/nbm/NetBeansManifestUpdateMojo.java [586:600]
String conditionallyAddAttribute(Manifest.Section section, String key, String value) {
Manifest.Attribute attr = section.getAttribute(key);
if (attr == null) {
attr = new Manifest.Attribute();
attr.setName(key);
attr.setValue(value != null ? value.replaceAll("\\s+", " ").trim() : "<undefined>");
try {
section.addConfiguredAttribute(attr);
} catch (ManifestException ex) {
getLog().error("Cannot update manifest (key=" + key + ")");
ex.printStackTrace();
}
}
return attr.getValue();
}