NPE Generating DocumentStructure

If the user set the field DocumentName to null, then he calls the DocumentStructure generation and defines a document version for the generation, the user will get an NPE.

java.lang.NullPointerException: Cannot invoke "String.length()" because "str" is null at java.base/java.lang.AbstractStringBuilder.<init>(AbstractStringBuilder.java:118) at java.base/java.lang.StringBuilder.<init>(StringBuilder.java:131) at org.eclipse.papyrus.model2doc.emf.template2structure.generator.AbstractDocumentStructureGenerator.updateGeneratedDocumentName(AbstractDocumentStructureGenerator.java:119) at org.eclipse.papyrus.model2doc.emf.template2structure.generator.AbstractDocumentStructureGenerator.generate(AbstractDocumentStructureGenerator.java:85) at org.eclipse.papyrus.model2doc.emf.template2structure.internal.command.GenerateDocumentStructureCommand.doExecute(GenerateDocumentStructureCommand.java:93) [...]