Do not allow empty captions and "nil" classes for figures

example-site/content/posts/image.md

@@ -1,6 +1,6 @@
 +++
 title = "Image"
-date = 2017-07-07T23:15:39-04:00
+date = 2017-07-07T23:32:14-04:00
 tags = []
 +++
 
@@ -11,7 +11,7 @@ tags = []
 
 # Unclickable image (works!)
 
-{{<figure src="/images/org-mode-unicorn-logo.png" caption="" class="nil">}}
+{{<figure src="/images/org-mode-unicorn-logo.png">}}
 
 **To be fixed**: The sub-headings in a post get exported as *Heading 1* instead of *Heading 2*.
 
@@ -33,13 +33,13 @@ So the sub-heading title and the post title both get the *Heading 1* tag and loo
 
 # Clickable image that opens the image (works!)
 
-Click below image to jump to the unicorn image. [{{<figure src="/images/org-mode-unicorn-logo.png" caption="" class="nil">}}](/images/org-mode-unicorn-logo.png)
+Click below image to jump to the unicorn image. [{{<figure src="/images/org-mode-unicorn-logo.png">}}](/images/org-mode-unicorn-logo.png)
 
 -   **NOTE:** `file:` has to be used in both Link and Description components of the Org link.
 
 
 # Image with `ATTR_HTML` [Issue # 17](https://github.com/kaushalmodi/ox-hugo/issues/17)
 
-{{<figure src="/images/org-mode-unicorn-logo.png" caption="" class="inset">}}
+{{<figure src="/images/org-mode-unicorn-logo.png" class="inset">}}
 
 [Discussion](https://github.com/kaushalmodi/ox-hugo/issues/17#issuecomment-313627728)

ox-hugo.el

@@ -198,8 +198,14 @@ and rewrite link paths to make blogging more seamless."
              (parent (org-export-get-parent link))
              (attr (org-export-read-attribute :attr_html parent))
              (class (plist-get attr :class)))
-	(format "{{<figure src=\"%s\" caption=\"%s\" class=\"%s\">}}"
-                path caption class)))
+	(format "{{<figure src=\"%s\"%s%s>}}"
+                path
+                (if (org-string-nw-p caption)
+                    (format " caption=\"%s\"" caption)
+                  "")
+                (if (org-string-nw-p class)
+                    (format " class=\"%s\"" class)
+                  ""))))
      ((string= type "coderef")
       (let ((ref (org-element-property :path link)))
 	(format (org-export-get-coderef-format ref contents)