Don't fail if there is no html part

app/models/email.rb

@@ -75,16 +75,18 @@ def html_part
 
   def html_part_images_inlined
     # TODO: Find a better home for this bit of code
-    t = TransformHtml.new(html_part)
-    doc = t.nokogiri
-    doc.search("img").each do |img|
-      if img["src"][0..3] == "cid:"
-        a = mail.attachments.find { |a| a.url == img["src"] }
-        # Construct the data url
-        img["src"] = "data:#{a.mime_type};base64,#{Base64.encode64(a.body.decoded)}" if a 
+    if html_part
+      t = TransformHtml.new(html_part)
+      doc = t.nokogiri
+      doc.search("img").each do |img|
+        if img["src"][0..3] == "cid:"
+          a = mail.attachments.find { |a| a.url == img["src"] }
+          # Construct the data url
+          img["src"] = "data:#{a.mime_type};base64,#{Base64.encode64(a.body.decoded)}" if a 
+        end
       end
+      doc.to_s
     end
-    doc.to_s
   end
 
   # First part with a particular mime type