Java Bug Fix Interview Question — Payment Retry Bug

Replacing nullable flags with explicit domain states

Suraj Mishra

Jun 09, 2026

∙ Paid

Scenario

You are building a payment platform.

When a payment fails due to a temporary issue:

network timeout
bank gateway unavailable
transient 5xx error

the system schedules a retry.

A new field was recently added:

Value Meaning

true. Retry allowed

false. Permanent failure

null. Unknown / not populate

A deployment goes live. and we see NullPointerException appearing intermittently.

Can you identify the bug?

The bug is caused by auto-unboxing a nullable Boolean into a primitive boolean.

In this line:

if (payment.getRetryable() == false) {
    return;
}

getRetryable() returns a Boolean object, but the == false comparison requires a primitive boolean.

The compiler effectively rewrites it as:

if (payment.getRetryable().booleanValue() == false) {
    return;
}

If retryable contains:

null

then Java attempts to execute:

null.booleanValue()

which throws a:

NullPointerException

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