Does a record with NULL data does not eat any storage on the harddrive?
You haven't mentioned your RDBMS system. You should always do this when asking any question.

Secondly, this would be easy to test. I'm sure that NULLs will add storage - maybe your question is about "How much storage exactly?"? 

Why not add 10,000 records of your structure with full data, then with NULL data and compare the size on disk. I'm fairly sure that the exact number will vary by RDBMS. There will be some overhead associated with fields even if empty.

There are many reasons why managers decide to do things - one of them is a lack of understanding of the technology. One solution might be to have another table "hanging" off your main table - only those records for which extra data is available will be in your subsidiary table?

To answer your last comment

"i have also looking at another solution, like having a table with a 
few columns, with each row is storing one property key with its value on 
the next column. But this ended up pushes the development back too far 
because of the complexity in data design and communication."


This sounds like you are considering an EAV-type design - NOT a good idea - see here and links from that post.