[2032] NPE when exporting LiteralString

Bug: #2032
Signed-off-by: Arthur Daussy <arthur.daussy@obeo.fr>

Author: adaussy

CHANGELOG.adoc

@@ -75,6 +75,7 @@ For example `ViewUsage` elements are no longer rendered in _parts_ compartments.
 - https://github.com/eclipse-syson/syson/issues/1998[#1998] [metamodel] Missing implicit TypeFeaturing.
 - https://github.com/eclipse-syson/syson/issues/2023[#2023] [diagrans] On diagrams, `ConnectionDefinition` graphical nodes are now correctly labelled as `«connection def»`.
 - https://github.com/eclipse-syson/syson/issues/2034[#2034] [import] Fix textual import to be able to annotate `Relationships`.
+- https://github.com/eclipse-syson/syson/issues/2032[#2032] [export] Fix NPE when exporting `LiteralString`.
 
 === Improvements
 

backend/application/syson-application/src/test/java/org/eclipse/syson/sysml/textual/SysMLElementSerializerTest.java

@@ -1257,6 +1257,9 @@ public void literalString() {
         literalStr.setValue("value");
 
         this.assertTextualFormEquals("\"value\"", literalStr);
+
+        literalStr.setValue(null);
+        this.assertTextualFormEquals("\"\"", literalStr);
     }
 
     @Test

backend/metamodel/syson-sysml-metamodel/src/main/java/org/eclipse/syson/sysml/textual/SysMLElementSerializer.java

@@ -631,7 +631,9 @@ private String toPreciseReal(double value) {
     public String caseLiteralString(LiteralString literal) {
         Appender builder = this.newAppender();
         builder.append("\"");
-        builder.append(literal.getValue().replace("\"", "\\\""));
+        if (literal.getValue() != null) {
+            builder.append(literal.getValue().replace("\"", "\\\""));
+        }
         builder.append("\"");
         return builder.toString();
     }

doc/content/modules/user-manual/pages/release-notes/2026.3.0.adoc

@@ -84,6 +84,8 @@ package Test {
 }
 ```
 
+** Fix a textual export problem while exporting `LiteralString` with no value.
+
 * In _Explorer_ view:
 
 ** Fix an issue where creating a new model using the _Create a new model_ action in the _Explorer_ view was not adding the ".sysml" extension to the model name.