Serializer fails on programmatically added property constant.

[schwerdf]

Summary

OSATE's Xtext serializer unexpectedly fails when serializing a property constant created programmatically via the object model.

Expected and Current Behavior

A plugin and AADL project reproducing this issue is checked in here.
The AADL project contains a property set Property_Constant_Add_Test, which contains one type. When the plugin is run on this property set it adds a new property constant of this type.
When trying to serialize the modified property set, the serializer fails with a ConflictingFormattingException bearing the message "Conflicting values for 'space': ' ' and ''."

Steps to Reproduce

1. Run the plugin from https://github.com/adventiumlabs/osate-serializer-bug.
2. Import the project Property_Constant_Add_Test and open the property set.
3. With the cursor in the editor window for the property set, go to "Sample Menu -> Sample Command" to activate the plugin.

Environment

• OSATE Version: 2.5.1.vfinal, installed as a plugin in vanilla Eclipse 2019-03
• Operating System: macOS 10.14