📝 doc: improve error message

src/state.rs

@@ -341,6 +341,7 @@ impl <'a> State <'a> {
 			},
 			Instruction::GetField (a, b, c) => {
 				let t = match self.reg (*b) {
+					Value::Nil => panic! ("R[B] must not be nil {}:{}", frame.block_idx, frame.program_counter),
 					Value::Table (t) => t,
 					_ => panic! ("R[B] must be a table"),
 				};