docs: @Override
      public void sawOpcode(int seen) {
          if (DEBUG) {
              System.out.println(getPC() + " " + Const.getOpcodeName(seen));
          }
          switch (seen) {
          case Const.IFNE:
          case Const.IFEQ: {
              OpcodeStack.Item top = stack.getStackItem(0);
              if (DEBUG) {
                  System.out.println("Stack top: " + top);
              }
              XMethod m = top.getReturnValueOf();
              if (m != null && "java.util.concurrent.ConcurrentHashMap".equals(m.getClassName())
                      && "containsKey".equals(m.getName())) {
                  lastQuestionableCheckTarget = getBranchTarget();
                  if (seen == Const.IFEQ) {
                      priority = LOW_PRIORITY;
                  } else if (seen == Const.IFNE) {
                      priority = NORMAL_PRIORITY;
                  }
              }
              break;
          }
          case Const.IFNULL:
          case Const.IFNONNULL: {
              OpcodeStack.Item top = stack.getStackItem(0);
              if (DEBUG) {
                  System.out.println("Stack top: " + top);
              }
              XMethod m = top.getReturnValueOf();
              if (DEBUG) {
                  System.out.println("Found null check");
              }
              if (m != null && "java.util.concurrent.ConcurrentHashMap".equals(m.getClassName()) && "get".equals(m.getName())) {
                  lastQuestionableCheckTarget = getBranchTarget();
                  if (seen == Const.IFNULL) {
                      priority = LOW_PRIORITY;
                  } else if (seen == Const.IFNONNULL) {
                      priority = NORMAL_PRIORITY;
                  }
              }
              break;
          }
          case Const.INVOKEVIRTUAL:
          case Const.INVOKEINTERFACE: {
              if ("java.util.concurrent.ConcurrentHashMap".equals(getDottedClassConstantOperand())) {
                  String methodName = getNameConstantOperand();
                  XClass xClass = getXClassOperand();
                  if (xClass != null && "put".equals(methodName)) {
                      if ((getPC() < lastQuestionableCheckTarget) && (lastQuestionableCheckTarget != -1)) {
                          bugReporter.reportBug(new BugInstance(this, "AT_OPERATION_SEQUENCE_ON_CONCURRENT_ABSTRACTION", priority)
                          .addClassAndMethod(this).addType(xClass.getClassDescriptor()).addCalledMethod(this)
                          .addSourceLine(this));
                      }
                  }
              }
              break;
          }
          default:
              break;
          }
      }