TheAlgorithms/Java · error · IllegalArgumentException

Input index cannot be null or negative!

Error message

Input index cannot be null or negative!

What it means

Thrown by FibonacciJavaStreams.calculate when index is null or compareTo(ZERO) < 0. The method computes the nth Fibonacci number via a BigDecimal stream reduction; a null index would NPE inside the comparator, and a negative index has no Fibonacci value. The guard combines both into a single message, so the same error text covers two distinct failure modes.

Source

Thrown at src/main/java/com/thealgorithms/maths/FibonacciJavaStreams.java:32

 * <ul>
 * <li>{@link com.thealgorithms.maths.FibonacciLoop} - Standard Iterative (Loop) approach</li>
 * <li>{@link com.thealgorithms.recursion.FibonacciSeries} - Naive Recursive approach</li>
 * <li>{@link com.thealgorithms.dynamicprogramming.Fibonacci} - Dynamic Programming approaches (Memoization, Bottom-Up, Optimized)</li>
 * <li>{@link com.thealgorithms.maths.FibonacciNumberGoldenRation} - Closed-form expression using Binet's formula</li>
 * <li>{@link com.thealgorithms.maths.FibonacciNumberCheck} - Utility to check if a given number is a Fibonacci number</li>
 * <li>{@link com.thealgorithms.matrix.matrixexponentiation.Fibonacci} - O(log n) Matrix Exponentiation approach</li>
 * </ul>
 * * @author caos321
 * @date 14 October 2021 (Thursday)
 */

public final class FibonacciJavaStreams {
    private FibonacciJavaStreams() {
    }

    public static Optional<BigDecimal> calculate(final BigDecimal index) {
        if (index == null || index.compareTo(BigDecimal.ZERO) < 0) {
            throw new IllegalArgumentException("Input index cannot be null or negative!");
        }

        if (index.compareTo(BigDecimal.ONE) < 0) {
            return Optional.of(BigDecimal.ZERO);
        }

        if (index.compareTo(BigDecimal.TWO) < 0) {
            return Optional.of(BigDecimal.ONE);
        }

        final List<BigDecimal> results = Stream.iterate(index, x -> x.compareTo(BigDecimal.ZERO) > 0, x -> x.subtract(BigDecimal.ONE))
                                             .reduce(List.of(), (list, current) -> list.isEmpty() || list.size() < 2 ? List.of(BigDecimal.ZERO, BigDecimal.ONE) : List.of(list.get(1), list.get(0).add(list.get(1))), (list1, list2) -> list1);

        return results.isEmpty() ? Optional.empty() : Optional.of(results.get(results.size() - 1));
    }
}

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Pass a non-null, non-negative BigDecimal such as calculate(BigDecimal.TEN).
2. If using Optional, unwrap safely: opt.orElseThrow() after a non-negative check.
3. Validate index != null && index.signum() >= 0 before calling.

Example fix

// before
Optional<BigDecimal> f = FibonacciJavaStreams.calculate(null);

// after
Optional<BigDecimal> f = FibonacciJavaStreams.calculate(BigDecimal.valueOf(10));

if (index == null || index.signum() < 0) {
    throw new IllegalArgumentException("Fibonacci index must be non-null and >= 0");
}
FibonacciJavaStreams.calculate(index);

static boolean isValidFibIndex(BigDecimal i) {
    return i != null && i.signum() >= 0;
}

When it happens

Trigger: Calling calculate(null) or calculate(BigDecimal.valueOf(-1)). The check fires before the early-return guards for index < 1 and index < 2, so a null or negative always hits this branch first.

Common situations: Optional/nullable BigDecimal from a parser not unwrapped; index read from input that accepted a minus sign; arithmetic producing a negative index; default null field passed.

Related errors

• Input 'n' must be a non-negative integer.
• Input 'n' must be a non-negative integer.
• Input must contain only '0' and '1'.
• Inputs cannot be null.
• Key must not be null

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/8a127f8c6f95d226. Report an issue: GitHub.