The merge operation in OData V2 can be used to update individual fields on an entity. The operation should perform an incremental update without replacing all the contents of an entry. In particular the request updates only the properties indicated in the request body, and leaves untouched any other property not mentioned in its current state.
When the camel-olingo2 component performs the merge operation all fields are updated - also the not mentioned properties. Those fields not mentioned in the request body are set to null by default.
This behavior is controlled by the EntityProvider write property called "isDataBasedPropertySerialization". By default this setting is set to false resulting in non present fields to be set to null by default. For merge operations this setting should be enabled by default in order to just update the mentioned fields in the request body.