This exception happens here:
    public void addBridgeForNodeIid(InstanceIdentifier<Node> nodeIid, OvsdbBridgeAugmentation bridge) {
        if (nodeIid != null && bridge != null) {
            nodeIidToBridgeMap.put(nodeIid, bridge);
        }
    }

It would seem the only way this can happen is if nodeIidToBridgeMap is null. nodeIidToEtc is initialized here:

    public void start() {
        try {
            createIdPool();
            configEntityCandidate = entityOwnershipService.registerCandidate(
                    new Entity(IfmConstants.INTERFACE_CONFIG_ENTITY, IfmConstants.INTERFACE_CONFIG_ENTITY));
            bindingEntityCandidate = entityOwnershipService.registerCandidate(
                    new Entity(IfmConstants.INTERFACE_SERVICE_BINDING_ENTITY,
                            IfmConstants.INTERFACE_SERVICE_BINDING_ENTITY));
            this.ifaceToTpMap = new ConcurrentHashMap<>();
            this.ifaceToNodeIidMap = new ConcurrentHashMap<>();
            this.nodeIidToBridgeMap = new ConcurrentHashMap<>();
            ifmStatusProvider.reportStatus(ServiceState.OPERATIONAL);
            LOG.info("InterfacemgrProvider Started");
        } catch (CandidateAlreadyRegisteredException e) {
            LOG.error("Failed to register entity {} with EntityOwnershipService", e.getEntity());
            ifmStatusProvider.reportStatus(e);
        } catch (InterruptedException | ExecutionException e) {
            LOG.error("Failed to create idPool for InterfaceMgr", e);
        }
    }

If an exception is thrown in the first three lines of the try block the hash maps will never be initialized. Can you please check if any of the LOG.error messages are present higher up in the log? Also, please check for "InterfacemgrProvider Started"?

NB: In general there is no reason for the hash map initializations to be in the try block. A patch should be raised to move them.

Sai, can you please attach the relevant logs from when this happened?

Closing since there are no logs attached.

Please attach the relevant logs and reopen the bug should you encounter it again.