code: public PrimitiveType getPrimitiveType(TypeMirror typeMirror) {
  		if (getPrimitiveFor(typeMirror) != null) {
  			return this.types.unboxedType(typeMirror);
  		}
  		return null;
  	}
docs: Return the {@link PrimitiveType} of the specified type or {@code null} if the type
  does not represent a valid wrapper type.
  @param typeMirror a type
  @return the primitive type or {@code null} if the type is not a wrapper type