Add fallback comments for generated composite fields and classes

Generated composite fields and the composite class itself were emitted
without a Javadoc comment when the XML carried no comment, producing
"no comment" warnings. Fall back to "The <name> field." and
"The <name> structure." respectively when the XML comment is absent,
while still using the XML comment when present.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: CesarCoelho

api-generator/generator-java/src/main/java/esa/mo/tools/stubgen/java/JavaClassWriter.java

@@ -144,7 +144,11 @@ public void addClassVariable(boolean isStatic, boolean isFinal, String scope, Co
 
     protected void addClassVariable(boolean isDeprecated, boolean isStatic, boolean isFinal, String scope,
             CompositeField field, boolean isObject, boolean isArray, String initialValue) throws IOException {
-        addMultilineComment(1, false, field.getComment(), false);
+        String fieldComment = field.getComment();
+        if (fieldComment == null || fieldComment.isEmpty()) {
+            fieldComment = "The " + field.getFieldName() + " field.";
+        }
+        addMultilineComment(1, false, fieldComment, false);
 
         StringBuilder buf = new StringBuilder(scope);
         buf.append(" ");

api-generator/generator-java/src/main/java/esa/mo/tools/stubgen/java/JavaCompositeClass.java

@@ -82,8 +82,12 @@ public void createCompositeClass(File folder, AreaType area, ServiceType service
         List<CompositeField> superCompElements = generator.createCompositeSuperElementsList(file, parentType);
 
         boolean abstractComposite = (composite.getShortFormPart() == null);
+        String compositeComment = composite.getComment();
+        if (compositeComment == null || compositeComment.isEmpty()) {
+            compositeComment = "The " + className + " structure.";
+        }
         file.addClassOpenStatement(className, !abstractComposite, abstractComposite,
-                parentClass, parentInterface, composite.getComment());
+                parentClass, parentInterface, compositeComment);
         String fqName = generator.createElementType(area.getName(), serviceName, className);
 
         if (!abstractComposite) {