Able to create task nodes without start node and end node in embedded subprocess

Description of problem:
In embedded subprocess we can create task nodes without start node and end node.We can build package and start process instance without any issue.
BPMN process attached to replicate issue.

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
1. Import attached BPMN process.
2. Build package and start server instance.

Actual results:
Process instance executed without any error.

Expected results:
Exception should be thrown while building package.

Additional info: