Background:

There is the possibility to create so called "standalone tasks" by either using  the Camunda Tasklist function "Create Task" or calling the REST-API ("POST /task/create").

Standalone tasks differ from regular process tasks e.g. by not belonging to a definition/not having an execution.

User Story (Required on creation):

As a developer, I want to be able to build a filter query that returns all existing standalone tasks using the task REST-API (e.g. Get List (POST))

Functional Requirements (Required before implementation):

• Query for standalone tasks via REST API
• Query for standalone tasks in filters
• Support querying within OR queries

Technical Requirements (Required before implementation):

• Add a new query option to the Task Query API like "isStandaloneTask"
• Consider the option in the task entity mappings
• Supported the option in task filters
• Make the option available in the REST APIs for querying (historic) tasks

Limitations of Scope (Optional):

Hints (optional):

Querying for the absence of a definition or execution by posting something like this to the REST-API:

#POST /task

{
 "processDefinitionId": null,
 "executionId": null
}

does not seem to do the job.
As a result, the query filter seems to be ignored and always all tasks are returned including the regular process tasks.