ObjectFlagProperty<T>  constructor 
- String name,
 - T? value, {
 - String? ifPresent,
 - String? ifNull,
 - bool showName = false,
 - DiagnosticLevel level = DiagnosticLevel.info,
 
Create a diagnostics property for values that can be present (non-null) or absent (null), but for which the exact value's Object.toString representation is not very transparent (e.g. a callback).
At least one of ifPresent or ifNull must be non-null.
Implementation
ObjectFlagProperty(
  String super.name,
  super.value, {
  this.ifPresent,
  super.ifNull,
  super.showName = false,
  super.level,
}) : assert(ifPresent != null || ifNull != null);