mv.visitVarInsn(ILOAD, 1);
mv.visitInsn(I2S);
mv.visitFieldInsn(PUTSTATIC, "pkg/Insns", "s", "S");
// checkcast
mv.visitInsn(ACONST_NULL);
mv.visitTypeInsn(CHECKCAST, "java/lang/String");
mv.visitInsn(ACONST_NULL);
mv.visitTypeInsn(CHECKCAST, "[[I");
// instanceof
mv.visitInsn(ACONST_NULL);
mv.visitTypeInsn(INSTANCEOF, "java/lang/String");