fix:in no classpath, something error in toString of CtExecutableRefer…

[sretake]

@Test()
void foo(){
    Launcher launcher = new Launcher();
    launcher.getEnvironment().setComplianceLevel(11);
    launcher.getEnvironment().setAutoImports(true);
    launcher.addInputResource(new VirtualFile("import java.util.List;\n" +
        "import org.apache.maven.api.model.Profile;\n" +
        "class A{\n" +
        "    public void run(List<Integer> list){\n" +
        "        list.stream().map(org.apache.maven.api.model.Profile::new);\n" +
        "    }\n" +
        "}\n"));
    CtModel ctModel = launcher.buildModel();
    List<CtExecutableReference> elements = ctModel.getElements(new TypeFilter<>(CtExecutableReference.class));
    for (CtExecutableReference element : elements) {
        try{
            element.toString();
        }catch(Exception e){
            e.printStackTrace();
        }
    }
}

[monperrus]

thanks @sretake, could you add the test in the PR?

[monperrus]

moving forward with this simple change, thanks @sretake