proguard does not create output jar

I'm running proguard on a single class file but the output.jar file is not created.

$ javap -c java-8-classes/BinaryNode.class | sed -n "139,150p;151q"
  public int hashCode();
    Code:
       0: aload_0
       1: getfield      #2                  // Field _data:[B
       4: ifnonnull     11
       7: iconst_m1
       8: goto          16
      11: aload_0
      12: getfield      #2                  // Field _data:[B
      15: arraylength
      16: ireturn

So unless I'm mistaken(?) it seems that BinaryNode::hashCode only needs _data field.

$ javap -c java-8-classes/BinaryNode.class | sed -n "5,6p;7q"
  protected final byte[] _data;

So I edited my config.pro accordingly:

$ cat config.pro
-injars java-8-classes/BinaryNode.class
-outjars output.jar
-verbose
-keep class com.fasterxml.jackson.databind.node.BinaryNode
{
    protected final byte[] _data;
    public int hashCode();
}
-allowaccessmodification

When I run proguard, output jar does not get created:

$ java -jar ../proguard/lib/proguard.jar -dontwarn @config.pro
ProGuard, version 7.1.0-beta2
Reading input...
Reading program directory [/home/oren/Documents/java-8-classes/BinaryNode.class] (filtered) # <---- OK??
Initializing...
<...>
Preparing output jar [/home/oren/Documents/output.jar] (filtered) # <---- WHY ???