Source:
<code>private static void executeCheckSig(Transaction txContainingThis, int index, Script script, LinkedList<byte[]> stack, int lastCodeSepLocation, int opcode, Set<VerifyFlag> verifyFlags) throws ScriptException { final boolean requireCanonical = verifyFlags.contains(VerifyFlag.STRICTENC) || verifyFlags.contains(VerifyFlag.DERSIG) || verifyFlags.contains(VerifyFlag.LOW_S); if (stack.size() < 2) throw new ScriptException("Attempted OP_CHECKSIG(VERIFY) on a stack with size < 2"); byte[] pubKey = stack.pollLast(); byte[] sigBytes = stack.pollLast(); byte[] prog = script.getProgram(); byte[] connectedScript = Arrays.copyOfRange(prog, lastCodeSepLocation, prog.length); UnsafeByteArrayOutputStream outStream = new UnsafeByteArrayOutputStream(sigBytes.length + 1); try { writeBytes(outStream, sigBytes); } catch (IOException e) { throw new RuntimeException(e); } connectedScript = removeAllInstancesOf(connectedScript, outStream.toByteArray()); boolean sigValid = false; try { TransactionSignature sig = TransactionSignature.decodeFromBitcoin(sigBytes, requireCanonical); Sha256Hash hash = txContainingThis.hashForSignature(index, connectedScript, (byte) sig.sighashFlags); sigValid = ECKey.verify(hash.getBytes(), sig, pubKey); } catch (Exception e1) { if (!e1.getMessage().contains("Reached past end of ASN.1 stream")) <START> log.warn("Signature checking failed! {}", e1); <END> } if (opcode == OP_CHECKSIG) stack.add(sigValid ? new byte[] {1} : new byte[] {}); else if (opcode == OP_CHECKSIGVERIFY) if (!sigValid) throw new ScriptException("Script failed OP_CHECKSIGVERIFY"); }</code><technical_language>I in this case "{}" stays unused, warn(String, Throwable) overload is used</technical_language>

Target:
private static void executeCheckSig(Transaction txContainingThis, int index, Script script, LinkedList<byte[]> stack, int lastCodeSepLocation, int opcode, Set<VerifyFlag> verifyFlags) throws ScriptException { final boolean requireCanonical = verifyFlags.contains(VerifyFlag.STRICTENC) || verifyFlags.contains(VerifyFlag.DERSIG) || verifyFlags.contains(VerifyFlag.LOW_S); if (stack.size() < 2) throw new ScriptException("Attempted OP_CHECKSIG(VERIFY) on a stack with size < 2"); byte[] pubKey = stack.pollLast(); byte[] sigBytes = stack.pollLast(); byte[] prog = script.getProgram(); byte[] connectedScript = Arrays.copyOfRange(prog, lastCodeSepLocation, prog.length); UnsafeByteArrayOutputStream outStream = new UnsafeByteArrayOutputStream(sigBytes.length + 1); try { writeBytes(outStream, sigBytes); } catch (IOException e) { throw new RuntimeException(e); } connectedScript = removeAllInstancesOf(connectedScript, outStream.toByteArray()); boolean sigValid = false; try { TransactionSignature sig = TransactionSignature.decodeFromBitcoin(sigBytes, requireCanonical); Sha256Hash hash = txContainingThis.hashForSignature(index, connectedScript, (byte) sig.sighashFlags); sigValid = ECKey.verify(hash.getBytes(), sig, pubKey); } catch (Exception e1) { if (!e1.getMessage().contains("Reached past end of ASN.1 stream")) log.warn("Signature checking failed!", e1); } if (opcode == OP_CHECKSIG) stack.add(sigValid ? new byte[] {1} : new byte[] {}); else if (opcode == OP_CHECKSIGVERIFY) if (!sigValid) throw new ScriptException("Script failed OP_CHECKSIGVERIFY"); }