Magento Migration Unable to serialize value from sales_flat_order_item

[zero_cool]

I'm getting error while Migrating data from 1.9.3.3 to 2.2.6 CE.

Error I'm getting is like below:

Could not unserialize data of sales_flat_order_item.product_options with record id 7.

I've checked that field there is broken value like : b:0;

Rather than this other fields have complete serialize data.

How can I fix this ??

Note : I've also more fields with universalize value.

Thanks If you help me with this.