allow DefaultFeatureValueProvider to omit optional parameters and features

plugins/org.yakindu.sct.generator.core/src/org/yakindu/sct/generator/core/features/AbstractDefaultFeatureValueProvider.java

@@ -34,7 +34,7 @@ public abstract class AbstractDefaultFeatureValueProvider implements
 		for (FeatureParameter parameter : parameters) {
 			FeatureParameterValue parameterValue = createParameterValue(
 					parameter, statechart);
-			if (parameterValue != null) {
+			if (parameterValue != null && parameterValue.getExpression() != null) {
 				config.getParameterValues().add(parameterValue);
 			}
 		}

plugins/org.yakindu.sct.generator.genmodel.ui/src/org/yakindu/sct/generator/genmodel/ui/wizard/ModelCreator.java

@@ -51,7 +51,7 @@ public class ModelCreator {
 		for (FeatureType featureType : featureTypes) {
 			FeatureConfiguration config = createFeatureConfiguration(
 					statechart, featureType);
-			if (config != null) {
+			if (config != null && !config.getParameterValues().isEmpty()) {
 				entry.getFeatures().add(config);
 			}
 		}