Who told you that "if the contract is not stamping, it can be null and void" ? That is not true. A contract is only void if it is against the Contracts Act 1950.
In this case, the vendor has not even signed the SPA. So, even if the purchaser has a copy in his lawyer's file, it still can't be stamped.
However, the purchaser can fall back on the letter of offer to purchase, where an earnest deposit has been paid. He can also refer to the correspondence where the SPA has been finalised, executed by him and forwarded to the vendor with the cheque for 10%, but the vendor now refuses to sign.
He may not be able to exercise his rights according to the terms of the SPA, but it does not mean that he cannot refer to the existence of a finalised SPA which he has signed and which the vendor refuses to do so. These are 2 different things.
Even if the purchaser requests for compensation, he can argue that it is customary for the 10% deposit to be refunded and for a further 10% to be paid as damages.
Basically, his rights are protected under common law.
Dear Dario, thank u for yr reply. Refer to the s&p stamping issue, I just want to confirm my understanding is correct. Does that mean that if purchaser signed s&p but vendor refused to sign, the purchaser can ask compensation from vendor (10% deposit paid to vendor + 10% of damages)?? Is that correct? Thank u