Interface connection

UVM
,
4

I try to retrieve an instance of the spy_if interface from the configuration database.
The variable found =1
This means that the get function is successful
But the spy_if_inst is still null
What missing in the code?

function void generator::build_phase (uvm_phase phase);
	super.build_phase(phase);
	$display("Before get(): spy_if_inst = %p", spy_if_inst);
	found = uvm_config_db#(virtual spy_if)::get(null, "", "spy_if_inst", spy_if_inst);
	$display("After get(): spy_if_inst = %p", spy_if_inst);
$display("found %b:",found);  
endfunction