Creates a new null layer and adds the AVLayer object to this collection. This is the same as choosing Layer > New > Null object.
duration Optional, the length of a still layer in seconds, a floating-point value.
If supplied, sets the du r at i on value of the new layer. Otherwise, the du r at i on value is set according to user preferences. By default, this is the same as the duration of the containing CompItem. To set another preferred value, choose Edit > Preferences > Import (Windows) or After Effects > Preferences > Import (Mac OS), and specify options under Still Footage.