http://xmlgraphics.apache.org/fop/: Apache FOP (Formatting Objects Processor) is the world's first print formatter driven by XSL formatting objects (XSL-FO) and the world's first output independent formatter. It is a Java application that reads a formatting object (FO) tree and renders the resulting pages to a specified output. Output formats currently supported include PDF, PCL, PS, AFP, TIFF, PNG, SVG, XML (area tree representation), Print, AWT and TXT. The primary output target is PDF. (Apache Software Foundation) 
public final class org.apache.fop.pdf.PDFNull implements org.apache.fop.pdf.PDFWritable
  minor version: 0
  major version: 59
  flags: flags: (0x0031) ACC_PUBLIC, ACC_FINAL, ACC_SUPER
  this_class: org.apache.fop.pdf.PDFNull
  super_class: java.lang.Object
{
  public static final org.apache.fop.pdf.PDFNull INSTANCE;
    descriptor: Lorg/apache/fop/pdf/PDFNull;
    flags: (0x0019) ACC_PUBLIC, ACC_STATIC, ACC_FINAL

  static void <clinit>();
    descriptor: ()V
    flags: (0x0008) ACC_STATIC
    Code:
      stack=2, locals=0, args_size=0
         0: .line 31
            new org.apache.fop.pdf.PDFNull
            dup
            invokespecial org.apache.fop.pdf.PDFNull.<init>:()V
            putstatic org.apache.fop.pdf.PDFNull.INSTANCE:Lorg/apache/fop/pdf/PDFNull;
            return
      LocalVariableTable:
        Start  End  Slot  Name  Signature

  private void <init>();
    descriptor: ()V
    flags: (0x0002) ACC_PRIVATE
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // org.apache.fop.pdf.PDFNull this
         0: .line 36
            aload 0 /* this */
            invokespecial java.lang.Object.<init>:()V
         1: .line 37
            return
        end local 0 // org.apache.fop.pdf.PDFNull this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    2     0  this  Lorg/apache/fop/pdf/PDFNull;

  public java.lang.String toString();
    descriptor: ()Ljava/lang/String;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
        start local 0 // org.apache.fop.pdf.PDFNull this
         0: .line 42
            ldc "null"
            areturn
        end local 0 // org.apache.fop.pdf.PDFNull this
      LocalVariableTable:
        Start  End  Slot  Name  Signature
            0    1     0  this  Lorg/apache/fop/pdf/PDFNull;

  public void outputInline(java.io.OutputStream, java.lang.StringBuilder);
    descriptor: (Ljava/io/OutputStream;Ljava/lang/StringBuilder;)V
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=3, args_size=3
        start local 0 // org.apache.fop.pdf.PDFNull this
        start local 1 // java.io.OutputStream out
        start local 2 // java.lang.StringBuilder textBuffer
         0: .line 47
            aload 2 /* textBuffer */
            aload 0 /* this */
            invokevirtual org.apache.fop.pdf.PDFNull.toString:()Ljava/lang/String;
            invokevirtual java.lang.StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
            pop
         1: .line 48
            return
        end local 2 // java.lang.StringBuilder textBuffer
        end local 1 // java.io.OutputStream out
        end local 0 // org.apache.fop.pdf.PDFNull this
      LocalVariableTable:
        Start  End  Slot        Name  Signature
            0    2     0        this  Lorg/apache/fop/pdf/PDFNull;
            0    2     1         out  Ljava/io/OutputStream;
            0    2     2  textBuffer  Ljava/lang/StringBuilder;
    Exceptions:
      throws java.io.IOException
    MethodParameters:
            Name  Flags
      out         
      textBuffer  
}
SourceFile: "PDFNull.java"