Is the field required ?
Source position: db.pas line 211
public property TFieldDef.Required : Boolean |
Required is set to True if the field requires a value when posting data to the dataset. If no value was entered, the dataset will raise an exception when the record is posted. The Required property is usually initialized based on the definition of the field in the underlying database. For SQL-based databases, a field declared as NOT NULL will result in a Required property of True.