null and empty paths in Annotation Path, Property Path, Navigation Property Path

Change text for restriction in section 14.4.1.3 Annotation Path to A non-null path MUST resolve to an annotation. Change text for restriction in section 14.4.1.5 Navigation Property Path to A non-null path MUST resolve to a model element whose type is an abstract or concrete entity type, or a collection of abstract or concrete entity types, e.g. a navigation property. Change text for restriction in section 14.4.1.6 Property Path to A non-null path MUST resolve to a model element whose type is an abstract or concrete primitive or complex type, or a collection of abstract or concrete primitive or complex types, e.g. a structural property.