I get "Exception in thread "main" java.util.UnknownFormatConversionException:" after compiling the code

Please I need some help with my code. I believe I have the same code as the instructor by the end of the video, however, when I compile I get the following error message:

Adding Exception in thread "main" java.util.UnknownFormatConversionException: Conversion = '.'
at java.util.Formatter.checkText(Formatter.java:2579)
at java.util.Formatter.parse(Formatter.java:2565)
at java.util.Formatter.format(Formatter.java:2501)
at java.util.Formatter.format(Formatter.java:2455)
at java.lang.String.format(String.java:2940)
at com.teamtreehouse.model.Song.toString(Song.java:28)
at java.util.Formatter$FormatSpecifier.printString(Formatter.java:2886)
at java.util.Formatter$FormatSpecifier.print(Formatter.java:2763)
at java.util.Formatter.checkText(Formatter.java:2579)
at java.util.Formatter.parse(Formatter.java:2565)
at java.util.Formatter.format(Formatter.java:2501)
at java.util.Formatter.format(Formatter.java:2455)
at java.lang.String.format(String.java:2940)
at com.teamtreehouse.model.Song.toString(Song.java:28)
at java.util.Formatter$FormatSpecifier.printString(Formatter.java:2886)
at java.util.Formatter$FormatSpecifier.print(Formatter.java:2763)
at java.util.Formatter.format(Formatter.java:2520)
at java.io.PrintStream.format(PrintStream.java:970)
at java.io.PrintStream.printf(PrintStream.java:871)
at Karaoke.main(Karaoke.java:13)

Song.java

package com.teamtreehouse.model;

public class Song{ private String mArtist; private String mTitle; private String mVideoUrl;

public Song(String artist, String title, String videoUrl){ mArtist = artist; mTitle = title; mVideoUrl = videoUrl; }

public String getArtist(){ return mArtist; }

public String getTitle(){ return mTitle; }

public String getVideoUrl(){ return mVideoUrl; }

@Override public String toString(){ return String.format("Song: %s by s%.", mTitle, mArtist); }

}

SongBook.java

package com.teamtreehouse.model;

import java.util.List; import java.util.ArrayList;

public class SongBook{ private List<Song> mSongs;

public SongBook(){ mSongs = new ArrayList<Song>(); }

public void addSong(Song song){ mSongs.add(song); }

public int getSongCount(){ return mSongs.size(); }

}

Karaoke.java

import com.teamtreehouse.model.Song; import com.teamtreehouse.model.SongBook;

public class Karaoke{

public static void main(String[] args){ Song song = new Song( "Michael Jackson", "Beat It", "https://www.youtube.com/watch?v=oRdxUFDoQe0");

SongBook songBook = new SongBook();
System.out.printf("Adding %s %n", song);
songBook.addSong(song);
System.out.printf("There are %d songs. %n", songBook.getSongCount());

}

}