skip empty preview card

src/main/java/de/jalin/fedipage/FediMedium.java

@@ -20,7 +20,7 @@ public class FediMedium implements Serializable {
 		this.mediumType = IMAGE;
 		this.description = "missing alt text";
 		this.mediumUrl = "unknown";
-		this.mediumImage = "assets/splash.jpg";
+		this.mediumImage = null;
 	}
 	
 	public String getMediumType() {

src/main/java/de/jalin/fedipage/JSONLoader.java

@@ -80,12 +80,9 @@ public class JSONLoader implements Serializable {
     				if (imageObject != null && imageObject instanceof String) {
     					medium.setMediumImage(jsonCard.getString("image"));
     					medium.setMediumImage(buildCacheUrl(jsonCard.getString("image")));
-    				} else {
-    					final String defaultImage = contextUrl + medium.getMediumImage();
-    					medium.setMediumImage(defaultImage);
-    				}
         				post.addFediMedium(medium);
     				}
+    			}
     		} else {
     			for (int mediaIdx=0; mediaIdx<mediaJsonArray.length(); mediaIdx++) {
     				final JSONObject mediumJsonObject = mediaJsonArray.getJSONObject(mediaIdx);