The phrase "declared null" is correct and can be used in written English.
It essentially means "declared void" or "declared invalid". It can be used to refer to a legal declaration of invalidity or invalidation of something. For example, "The court declared the contract null due to the parties not meeting the required qualifications."
"Our position is that the declaration should be disregarded by the international community and declared null and void," said Vitaly I. Churkin, Russia's ambassador to the United Nations.
Discussion narrowed and all alternatives were declared null and void.
This meant that more than a thousand N.L.R.B. decisions were suddenly declared null and void.
La Nación, in Argentina, argued that this World Cup should be "declared null and void".
Uganda's anti-gay law was declared null and void on Friday 1 August.
"The line the judges have taken thus far is that this could be grounds to have the prosecution declared null".
Tax authorities are increasingly able to declare null and void any transaction whose sole purpose is the avoidance of tax.
Nullification crisis, in U.S. history, confrontation between the state of South Carolina and the federal government in 1832 33 over the former's attempt to declare null and void within the state the federal Tariffs of 1828 and 1832.
Greenville strongly opposed nullification (in U.S. history, a doctrine holding that a state, within its territorial jurisdiction, has the right to declare null and void any federal law that violates its voluntary compact embodied in the Constitution) in 1832 and secession from the Union in 1860.
Gingrich began the annulment process, which may take years, in 2002 with a request that the Archdiocese of Atlanta declare "null" his marriage to his second wife, Marianne Gingrich.
Taylor meant by this doctrine to strengthen and make secure the system of slavery, from which he personally profited, since Virginia and the other Southern states would always be free to declare null and void any federal law infringing on slave-holders' "rights".
