Changed IrcFormatSerializer to fix bug #16224

SpannableString is initialized with the output of IrcFormatDeserializer::formatString. As SpannableString does not allow null inputs, we have to adapt this.

app/src/main/java/de/kuschku/util/irc/format/IrcFormatDeserializer.java

@@ -110,9 +110,9 @@ public class IrcFormatDeserializer {
      * @param str mIRC formatted String
      * @return a CharSequence with Android’s span format representing the input string
      */
-    @Nullable
+    @NonNUll
     public CharSequence formatString(@Nullable String str) {
-        if (str == null) return null;
+        if (str == null) return "";
 
         SpannableStringBuilder plainText = new SpannableStringBuilder();
         FormatDescription bold = null;