Bugfix: NPE when using Assignments within Expressions

plugins/org.yakindu.sct.model.sexec.interpreter/src/org/yakindu/sct/model/sexec/interpreter/stext/StextStatementInterpreter.xtend

@@ -76,7 +76,7 @@ class StextStatementInterpreter extends AbstractStatementInterpreter {
 			var operator = AbstractStatementInterpreter::assignFunctionMap.get(assignment.operator.getName())
 			context.setVariableValue(scopeVariable.name, evaluate(operator, scopeVariable.getValue,result))
 		}
-		null		
+		result		
 	}
 	
 	
@@ -89,6 +89,10 @@ class StextStatementInterpreter extends AbstractStatementInterpreter {
 		if (e.feature instanceof VariableDefinition) e.feature else null
 	}
 	
+	def dispatch variable(AssignmentExpression e) {
+		return e.varRef.variable as EObject
+	}
+	
 
 	def dispatch event(ElementReferenceExpression e) {
 		if (e.reference instanceof EventDefinition) e.reference else null