code: protected final int isLocalCollection(OpcodeStack.Item item) throws ClassNotFoundException {
          Comparable<?> aliasReg = (Comparable<?>) item.getUserValue();
          if (aliasReg instanceof Integer) {
              return ((Integer) aliasReg).intValue();
          }
  
          int reg = item.getRegisterNumber();
          if (reg < 0) {
              return -1;
          }
  
          JavaClass cls = item.getJavaClass();
          if ((cls != null) && cls.implementationOf(collectionClass)) {
              return reg;
          }
  
          return -1;
      }
docs: determines if the stack item refers to a collection that is stored in a local variable
  
  @param item
  the stack item to check
  
  @return the register number of the local variable that this collection refers to, or -1
  @throws ClassNotFoundException
  if the items class cannot be found