Please see the following code sample.
If parametrized class below

class MyClass<T> { }

is given to annotation processor that checks spec assertion:

@SupportedAnnotationTypes("*")
@SupportedSourceVersion(SourceVersion.RELEASE_6)
public class MyProcessor extends AbstractProcessor {

    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
        Set<? extends Element> rootElements = roundEnv.getRootElements();
        if (rootElements.size() > 0) {
            performCheck(rootElements);
        }
        return true;
    }

    private void performCheck(Set<? extends Element> rootElements) {
        TypeElement typeElement = ElementFilter.typesIn(rootElements).iterator().next();
        TypeParameterElement typeParameterElement = typeElement.getTypeParameters().get(0);
        // Element getEnclosingElement():
        // If this is a type parameter, {@code null} is returned.
        Element enclosingElement = typeParameterElement.getEnclosingElement();
        assert enclosingElement == null :
                "As spec for getEnclosingElement() says, enclosing element must be null for type parameter";
    }
}

We get:
java.lang.AssertionError: As spec for getEnclosingElement() says, enclosing element must be null for type parameter

Please don't forget to give -ea option to VM to enable asserts.