Class "Abstract Edit ConfigurationItem Action"

I’m trying to add custom configuration to my plugin.

In all examples I’ve found implementing the class AbstractEditConfigurationItemAction, only doValidation() and doExection() methods are overriden.

In doExecution(), the examples make use of AbstractEditConfigurationItemAction.getFieldConfig() to retrieve information about the custom field.

However for me, .getFieldConfig() returns null.

I checked the source, .getFieldConfig() depends on a Long field fieldConfigId(). In AbstractEditConfigurationItemAction, it is only set by public method setFieldConfigId(Long).

I override this method and found out no one invoked it. So fieldConfigId is null, and .getFieldConfig() will return null.

What am I missing?