code: @Override
      public void visitCode(Code obj) {
          Method m = getMethod();
          stack.resetForMethodEntry(this);
          initializedRegs.clear();
          modifyRegs.clear();
          Type[] argTypes = m.getArgumentTypes();
          int arg = m.isStatic() ? 0 : 1;
          for (Type argType : argTypes) {
              String argSig = argType.getSignature();
              initializedRegs.set(arg);
              arg += SignatureUtils.getSignatureSize(argSig);
          }
          nullStoreToLocation.clear();
          super.visitCode(obj);
  
          for (Integer pc : nullStoreToLocation.values()) {
              bugReporter.reportBug(new BugInstance(this, BugType.AIOB_ARRAY_STORE_TO_NULL_REFERENCE.name(), HIGH_PRIORITY).addClass(this).addMethod(this)
                      .addSourceLine(this, pc.intValue()));
          }
      }
docs: overrides the visitor to collect parameter registers
  
  @param obj
  the code block of the currently parsed method