code: protected String getInvalidWritableVariableAccessMessage(XVariableDeclaration variable, XAbstractFeatureCall featureCall, IResolvedTypes resolvedTypes) {
  		// TODO this should be part of a separate validation service
  		XClosure containingClosure = EcoreUtil2.getContainerOfType(featureCall, XClosure.class);
  		if (containingClosure != null && !EcoreUtil.isAncestor(containingClosure, variable)) {
  			return String.format("Cannot %srefer to the non-final variable %s inside a lambda expression", getImplicitlyMessagePart(featureCall), variable.getSimpleName());
  		}
  		return null;
  	}
docs: Provide the error message for mutable variables that may not be captured in lambdas.
  
  @param variable the writable variable declaration
  @param featureCall the reference to the variable
  @param resolvedTypes type information