Bug fix in tags filter: Treat SPC selection correctly.

* lisp/org-agenda.el (org-agenda-filter-make-matcher-tag-exp): Fix
filtering for any tag at all.

doc/org-manual.org

@@ -9033,8 +9033,8 @@ the estimated effort of an entry (see [[*Effort Estimates]]).
 #+vindex: org-agenda-effort-filter-preset
 #+vindex: org-agenda-regexp-filter-preset
 Agenda built-in or custom commands are statically defined.  Agenda
-filters and limits provide allow to flexibly narrow down the list of
-agenda entries.
+filters and limits allow to flexibly narrow down the list of agenda
+entries.
 
 /Filters/ only change the visibility of items, are very fast and are
 mostly used interactively[fn:96]. You can switch quickly between
@@ -9073,7 +9073,7 @@ filter elements are accumulated.
   command then hides all entries that do not contain or inherit this
   tag.  Pressing {{{kbd(+)}}} or {{{kbd(-)}}} at the prompt switches
   between filtering for and against the next tag.  To clear the
-  filter, press {{{kbd(\)}}} at the prompt.
+  filter, call the command again and press {{{kbd(\)}}} at the prompt.
 
 - {{{kbd(<)}}} (~org-agenda-filter-by-category~) ::
 
@@ -9111,7 +9111,8 @@ filter elements are accumulated.
   larger-or-equal than the selected value.  For application of the
   operator, entries without a defined effort are treated according to
   the value of ~org-sort-agenda-noeffort-is-high~.  To clear the
-  filter, press {{{kbd(_)}}} again at the operator prompt.
+  filter, call the command again and press {{{kbd(_)}}} again at the
+  operator prompt.
 
 - {{{kbd(^)}}} (~org-agenda-filter-by-top-headline~) ::
 

lisp/org-agenda.el

@@ -7912,7 +7912,7 @@ function to set the right switches in the returned form."
     (dolist (x tags (cons (if (eq op ?-) 'and 'or) form))
       (let* ((tag (substring x 1))
 	     (f (cond
-		 ((string= "" tag) '(not tags))
+		 ((string= "" tag) 'tags)
 		 ((and (string-match-p "\\`{" tag) (string-match-p "}\\'" tag))
 		  ;; TAG is a regexp.
 		  (list 'org-match-any-p (substring tag 1 -1) 'tags))