getParentValue method
Get 1st parent value of child
;
Implementation
V? getParentValue(K? child, {bool includePurgedEntries = false}) {
if (child == null) return null;
var parent = getParentKey(child);
return parent != null
? (includePurgedEntries
? getAlsoFromPurgedEntries(parent)
: get(parent))
: null;
}