Add !v.isEmpty() for value String

Author: Yauhenikapl

core/esmf-aspect-model-java-generator/src/main/java/org/eclipse/esmf/aspectmodel/java/AspectModelJavaUtil.java

@@ -698,7 +698,7 @@ public static String optionalExpression(
          final String modifiedExpression = expression.replace( target, "v" );
 
          return "Optional.ofNullable(matcher.group(" + groupNum + "))"
-               + ".filter(v -> v != null)"
+               + ".filter(v -> !v.isEmpty())"
                + ".map(v -> Integer.valueOf(v))"
                + ".map(v -> "
                + modifiedExpression

core/esmf-aspect-model-java-generator/src/test/java/org/eclipse/esmf/aspectmodel/java/AspectModelJavaGeneratorTest.java

@@ -259,7 +259,7 @@ void testGenerateAspectWithOptionalPropertyAndEntityWithSeparateFiles() throws I
             .orElseThrow( () -> new AssertionError( "Constructor not found in ProductionPeriodEntity" ) );
       String constructorBody = constructor.getBody().toString();
       assertThat( constructorBody ).contains( "Optional.ofNullable(" );
-      assertThat( constructorBody ).contains( ".filter(v -> v != null)" );
+      assertThat( constructorBody ).contains( ".filter(v -> !v.isEmpty())" );
       assertThat( constructorBody ).contains( "_datatypeFactory.newXMLGregorianCalendarDate(" );
    }