Update Machine.java

mutants/mutant-5/swen90006/machine/Machine.java

@@ -235,6 +235,9 @@ public class Machine
 	int rs2 = parseReg(toks[3]);
 	do_div(rd,rs1,rs2);
       } else if (toks[0].equals(INSTRUCTION_RETURN)){
+          if (toks.length != 2){
+	  throw new InvalidInstructionException();
+	}
 	int rs = parseReg(toks[1]);
 	count++;
 	return regs[rs];