While validating topology in either ArcCatalog or ArcMap, the following error message is raised:
"Validate Topology failed.
A failure was detected inside the topology engine overlay processor. [error id: -2147220465]
The value of the subtype code is NULL.[(class name: <objectclass_name>, oid: <ObjectID>)]"
The feature identified by the error message has a subtype value of null. Null subtype values are not supported by the geodatabase.
Solution or Workaround
If a subtype field is defined for a feature class, each feature in that feature class must have a valid subtype value. Features for which a valid subtype value does not exist will cause the validating of the topology to fail.
Instances may arise where features do not have a valid subtype value. A new subtype value can be added to act as a placeholder for the null field value. Depending on the subtype values already in place, the new subtype value could be 0, 1, 9999, etc. Creating the new subtype and assigning it all features with a Null subtype null will allow the validate to proceed.