fixes issue #600 (#606)

- improves documentation for HaveValue with respect to nil and negation.

docs/index.md

@@ -1356,7 +1356,7 @@ Any other comparator is an error.
 
 #### HaveValue(matcher types.GomegaMatcher)
 
-`HaveValue` applies `MATCHER` to the value that results from dereferencing `ACTUAL` in case of a pointer or an interface, or otherwise `ACTUAL` itself. Pointers and interfaces are dereferenced multiple times as necessary, with a limit of at most 31 dereferences.
+`HaveValue` applies `MATCHER` to the value that results from dereferencing `ACTUAL` in case of a pointer or an interface, or otherwise `ACTUAL` itself. Pointers and interfaces are dereferenced multiple times as necessary, with a limit of at most 31 dereferences. It will fail if the pointer value is `nil`:
 
 ```go
 Expect(ACTUAL).To(HaveValue(MATCHER))
@@ -1372,6 +1372,12 @@ Expect(i).To(HaveValue(Equal(42)))
 
 `HaveValue` can be used, for instance, in tests and custom matchers where the it doesn't matter (as opposed to `PointTo`) if a value first needs to be dereferenced or not. This is especially useful to custom matchers that are to be used in mixed contexts of pointers as well as non-pointers.
 
+Please note that negating the outcome of `HaveValue(nil)` won't suppress any error; for instance, in order to assert not having a specific value while still accepting `nil` the following matcher expression might be used:
+
+```go
+Or(BeNil(), Not(HaveValue(...)))
+```
+
 ### Working with HTTP responses
 
 #### HaveHTTPStatus(expected interface{})