Fix `org-backward-paragraph' on an empty heading

* lisp/org.el (org-backward-paragraph): Fix behavior on greater
  elements without contents.

* testing/lisp/test-org.el (test-org/backward-paragraph): Add test.

Reported-by: Omar Antolin <omar.antolin@gmail.com>
<http://lists.gnu.org/archive/html/emacs-orgmode/2017-10/msg00099.html>

2 files changed, 11 insertions, 6 deletions

diff --git a/lisp/org.el b/lisp/org.el
index 35405b4..3120fae 100644
--- a/lisp/org.el
+++ b/lisp/org.el
@@ -24230,10 +24230,11 @@ convenience:
 	(backward-char)
 	(org-backward-paragraph))
        ((<= (point) post-affiliated) (goto-char begin))
+       ;; Special behavior: on a table or a property drawer, move to
+       ;; its beginning.
        ((memq type '(node-property table-row))
 	(goto-char (org-element-property
 		    :post-affiliated (org-element-property :parent element))))
-       ((memq type '(property-drawer table)) (goto-char begin))
        (special?
 	(if (<= (point) contents-begin) (goto-char post-affiliated)
 	  ;; Inside a verse block, see blank lines as paragraph
@@ -24244,8 +24245,7 @@ convenience:
 	      (skip-chars-forward " \r\t\n" origin)
 	      (if (= (point) origin) (goto-char contents-begin)
 		(beginning-of-line))))))
-       ((eq type 'paragraph)
-	(goto-char contents-begin)
+       ((eq type 'paragraph) (goto-char contents-begin)
 	;; When at first paragraph in an item or a footnote definition,
 	;; move directly to beginning of line.
 	(let ((parent-contents
@@ -24253,9 +24253,9 @@ convenience:
 		:contents-begin (org-element-property :parent element))))
 	  (when (and parent-contents (= parent-contents contents-begin))
 	    (beginning-of-line))))
-       ;; At the end of a greater element, move to the beginning of the
-       ;; last element within.
-       ((>= (point) contents-end)
+       ;; At the end of a greater element, move to the beginning of
+       ;; the last element within.
+       ((and contents-end (>= (point) contents-end))
 	(goto-char (1- contents-end))
 	(org-backward-paragraph))
        (t (goto-char (or post-affiliated begin))))
diff --git a/testing/lisp/test-org.el b/testing/lisp/test-org.el
index 4023ec4..0ac3e60 100644
--- a/testing/lisp/test-org.el
+++ b/testing/lisp/test-org.el
@@ -3607,6 +3607,11 @@ SCHEDULED: <2017-05-06 Sat>
   (should
    (org-test-with-temp-text "#+BEGIN_<point>EXAMPLE\nL1\n#+END_EXAMPLE"
      (org-backward-paragraph)
+     (bobp)))
+  ;; Pathological case: on an empty heading, move to its beginning.
+  (should
+   (org-test-with-temp-text "* <point>H"
+     (org-backward-paragraph)
      (bobp))))
 
 (ert-deftest test-org/forward-element ()