diff --git a/youtube_dl/extractor/skillshare.py b/youtube_dl/extractor/skillshare.py
index ab54ecea1..0f65667e6 100644
--- a/youtube_dl/extractor/skillshare.py
+++ b/youtube_dl/extractor/skillshare.py
@@ -1,16 +1,19 @@
 from __future__ import unicode_literals
 
-from datetime import datetime
 import json
 
 from .common import InfoExtractor
 from ..compat import compat_str
-from ..utils import ExtractorError
-from ..utils import int_or_none
+from ..utils import (
+    ExtractorError,
+    int_or_none,
+    try_get,
+    unified_timestamp
+)
 
 
 class SkillshareBaseIE(InfoExtractor):
-    _NETRC_MACHINE = 'udemy'
+    _NETRC_MACHINE = "skillshare"
 
     _TN_RE = r"uploads/video/thumbnails/[0-9a-f]+/(?P<width>[0-9]+)-(?P<height>[0-9]+)"
     _LOGIN_URL = "https://api.skillshare.com/login"
@@ -66,7 +69,7 @@ class SkillshareCourseIE(SkillshareBaseIE):
         class_json = self._download_json(self._CLASS_URL % class_id,
                                          None,
                                          note="Getting class details",
-                                         errnote="Error getting class details")
+                                         errnote="Downloading class JSON")
 
         if class_json.get("enrollment_type", 0) > self._user_type:
             raise ExtractorError("This course requires a premium account and thus can't be downloaded")
@@ -79,10 +82,11 @@ class SkillshareCourseIE(SkillshareBaseIE):
         videos = []
         for lesson_json in lessons_json:
             lesson_thumbnail_urls = [
-                lesson_json.get("video_thumbnail_url", ""),
-                lesson_json.get("video_thumbnail_url", ""),
-                lesson_json.get("image_thumbnail", "")
+                lesson_json.get("video_thumbnail_url"),
+                lesson_json.get("video_thumbnail_url"),
+                lesson_json.get("image_thumbnail")
             ]
+            lesson_thumbnail_urls = filter(None, lesson_thumbnail_urls)
             lesson_thumbnails_json = []
             for lesson_thumbnail_url in lesson_thumbnail_urls:
                 lesson_thumbnails_json.append({
@@ -90,33 +94,33 @@ class SkillshareCourseIE(SkillshareBaseIE):
                     "width": int_or_none(self._search_regex(self._TN_RE, lesson_thumbnail_url, "width", fatal=False)),
                     "height": int_or_none(self._search_regex(self._TN_RE, lesson_thumbnail_url, "height", fatal=False)),
                 })
+            if not lesson_thumbnails_json:
+                lesson_thumbnails_json = None
 
-            try:
-                lesson_timestamp_dt = datetime.strptime(lesson_json.get("create_time", ""), "%Y-%m-%d %H:%M:%S")
-                lesson_timestamp = int(lesson_timestamp_dt.strftime("%s"))
-            except ValueError:
-                lesson_timestamp = None
+            lesson_categories = [class_json.get("category")]
+            if lesson_categories == [None]:
+                lesson_categories = None
 
             videos.append({
-                "id": str(lesson_json["id"]),
+                "id": compat_str(lesson_json["id"]),
                 "title": lesson_json.get("title"),
-                "url": self._VIDEO_URL % str(lesson_json["id"]),
+                "url": self._VIDEO_URL % compat_str(lesson_json["id"]),
                 "ext": "mp4",
                 "thumbnails": lesson_thumbnails_json,
-                "uploader": class_json["_embedded"].get("teacher", {}).get("full_name"),
-                "creator": class_json["_embedded"].get("teacher", {}).get("full_name"),
-                "timestamp": lesson_timestamp,
-                "uploader_id": str(class_json["_embedded"].get("teacher", {}).get("username", 0)),
-                "categories": [class_json.get("category")],
-                "chapter": lesson_json.get("_links", {}).get("unit", {}).get("title"),
+                "uploader": try_get(class_json, lambda x: x["_embedded"]["teacher"]["full_name"]),
+                "creator": try_get(class_json, lambda x: x["_embedded"]["teacher"]["full_name"]),
+                "timestamp": unified_timestamp(lesson_json.get("create_time")),
+                "uploader_id": compat_str(try_get(class_json, lambda x: x["_embedded"]["teacher"]["username"])),
+                "categories": lesson_categories,
+                "chapter": try_get(lesson_json, lambda x: x["_links"]["unit"]["title"]),
                 "chapter_id": compat_str(lesson_json.get("unit_id"))
             })
 
         return {
             "id": class_id,
-            "title": class_json.get("title"),
-            "uploader": class_json["_embedded"].get("teacher", {}).get("full_name"),
-            "uploader_id": str(class_json["_embedded"].get("teacher", {}).get("username", 0)),
+            "title": class_json["title"],
+            "uploader": try_get(class_json, lambda x: x["_embedded"]["teacher"]["full_name"]),
+            "uploader_id": compat_str(try_get(class_json, lambda x: x["_embedded"]["teacher"]["username"])),
             "_type": "playlist",
             "entries": videos
         }