TheAlgorithms/Java · error · NullPointerException

Arguments must not be null

Error message

Arguments must not be null

What it means

Thrown by BitwiseGCD.gcdBig(BigInteger a, BigInteger b) when either argument is null. The BigInteger-backed gcd cannot compute a.abs() or b.abs() on a null reference, so the method fails fast with a NullPointerException rather than letting the NPE surface deeper inside BigInteger with a less clear trace. Pass non-null BigInteger instances (BigInteger.ZERO is valid).

Source

Thrown at src/main/java/com/thealgorithms/bitmanipulation/BitwiseGCD.java:129

            if (result == 1L) {
                return 1L; // early exit
            }
        }
        return result;
    }

    /**
     * BigInteger-backed gcd that works for the full integer range (and beyond).
     * This is the recommended method when inputs may be Long.MIN_VALUE or when you
     * need an exact result even if it is greater than Long.MAX_VALUE.
     * @param a first value (may be negative)
     * @param b second value (may be negative)
     * @return non-negative gcd as a {@link BigInteger}
     */
    public static BigInteger gcdBig(BigInteger a, BigInteger b) {

        if (a == null || b == null) {
            throw new NullPointerException("Arguments must not be null");
        }
        return a.abs().gcd(b.abs());
    }

    /**
     * Convenience overload that accepts signed-64 inputs and returns BigInteger gcd.
     */
    public static BigInteger gcdBig(long a, long b) {
        return gcdBig(BigInteger.valueOf(a), BigInteger.valueOf(b));
    }

    /**
     * int overload for convenience.
     */
    public static int gcd(int a, int b) {
        return (int) gcd((long) a, (long) b);
    }
}

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Ensure both arguments are non-null; substitute BigInteger.ZERO (or another sensible default) for missing values.
2. Use Objects.requireNonNull(a, 'a') at the call site for a clearer message.
3. Validate the source (Optional/map lookup) before calling.

Example fix

// before
BitwiseGCD.gcdBig(maybeNullA, maybeNullB);  // throws NPE

// after
BigInteger a = Objects.requireNonNullElse(maybeNullA, BigInteger.ZERO);
BigInteger b = Objects.requireNonNullElse(maybeNullB, BigInteger.ZERO);
BitwiseGCD.gcdBig(a, b);

Objects.requireNonNull(a, "a");
Objects.requireNonNull(b, "b");
BitwiseGCD.gcdBig(a, b);

public static boolean nonNullArgs(BigInteger a, BigInteger b) {
    return a != null && b != null;
}

try {
    return BitwiseGCD.gcdBig(a, b);
} catch (NullPointerException e) {
    return BitwiseGCD.gcdBig(
        Objects.requireNonNullElse(a, BigInteger.ZERO),
        Objects.requireNonNullElse(b, BigInteger.ZERO));
}

When it happens

Trigger: Calling `gcdBig(null, BigInteger.TEN)` or `gcdBig(BigInteger.ONE, null)`. The guard `a == null || b == null` triggers before any computation; null is the only invalid input (any BigInteger value, including ZERO, is accepted).

Common situations: BigInteger values loaded from a map/optional that returned null; unboxing of a boxed reference that was never set; chaining from a parser that yields null on malformed input.

Related errors

• Absolute value of Long.MIN_VALUE does not fit into signed lo
• Maze must not be null or empty.
• Invalid BCD digit: {}
• Value out of bounds for BCD representation: {}
• Shift amount cannot be negative: {}

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/cc028ba10681f07e. Report an issue: GitHub.