@ I compile your 4.21-flex,but get some error.
25>H:\Source\ue4_gameworks\UnrealEngine\Engine\Source\Editor\BehaviorTreeEditor\Private\DetailCustomizations\BlackboardSelectorDetails.cpp(173): error C4800: Implicit conversion from ‘const wchar_t *’ to bool. Possible information loss
25> H:\Source\ue4_gameworks\UnrealEngine\Engine\Source\Editor\BehaviorTreeEditor\Private\DetailCustomizations\BlackboardSelectorDetails.cpp(173): note: consider using explicit cast or comparison to nullptr to avoid warning
25> [2/235] Module.DetailCustomizations.1_of_4.cpp
25>H:\Source\ue4_gameworks\UnrealEngine\Engine\Source\Runtime\Core\Public\Misc/Attribute.h(43): error C4800: Implicit conversion from ‘const OtherType’ to bool. Possible information loss