TheAlgorithms/Java · error · IllegalArgumentException

Input array cannot be null

Error message

Input array cannot be null

What it means

Thrown by RangeSumQuery.buildPrefixSum(nums) when nums is null. Unlike PrefixSum, this is a static utility that returns a fresh prefix-sum array; null input has no length to iterate. Empty arrays (length 0) are allowed and yield a size-1 prefix array.

Source

Thrown at src/main/java/com/thealgorithms/prefixsum/RangeSumQuery.java:43

 *
 * @author Ruturaj Jadhav, <a href="https://github.com/ruturajjadhav07">ruturajjadhav07</a>
 */
public final class RangeSumQuery {

    private RangeSumQuery() {
        // Utility class; prevent instantiation
    }

    /**
     * Computes the prefix sum array for efficient range queries.
     *
     * @param nums The input integer array.
     * @return Prefix sum array where prefixSum[i+1] = sum of nums[0..i].
     * @throws IllegalArgumentException if nums is null.
     */
    public static int[] buildPrefixSum(int[] nums) {
        if (nums == null) {
            throw new IllegalArgumentException("Input array cannot be null");
        }

        int n = nums.length;
        int[] prefixSum = new int[n + 1];
        for (int i = 0; i < n; i++) {
            prefixSum[i + 1] = prefixSum[i] + nums[i];
        }
        return prefixSum;
    }

    /**
     * Returns the sum of elements from index left to right (inclusive)
     * using the provided prefix sum array.
     *
     * @param prefixSum The prefix sum array computed using buildPrefixSum.
     * @param left      The start index (inclusive).
     * @param right     The end index (inclusive).
     * @return The sum of elements in the range [left, right].

View on GitHub (pinned to fdfb9a395b)

Solutions

1. Null-check at the caller; pass new int[0] if emptiness is acceptable.
2. Make the producer return an empty array instead of null (null-object pattern).
3. Wrap with Objects.requireNonNull(nums, "nums") for a clearer NPE if null is truly a bug.

Example fix

// before
int[] ps = RangeSumQuery.buildPrefixSum(data); // data may be null

// after
int[] safe = data == null ? new int[0] : data;
int[] ps = RangeSumQuery.buildPrefixSum(safe);

int[] safe = nums == null ? new int[0] : nums;
int[] ps = RangeSumQuery.buildPrefixSum(safe);

static boolean usable(int[] a) {
    return a != null; // empty allowed
}

try {
    int[] ps = RangeSumQuery.buildPrefixSum(nums);
} catch (IllegalArgumentException e) {
    logger.warn("Null input to buildPrefixSum");
}

When it happens

Trigger: RangeSumQuery.buildPrefixSum(null), or buildPrefixSum(someArray) where someArray was never assigned.

Common situations: Passing a possibly-null field from a record/DTO; chaining a method that returns null on failure into buildPrefixSum; missing JSON field deserializing to null.

Related errors

• Prefix sum array cannot be null
• Input array cannot be null
• Input matrix cannot be null or empty
• Input array cannot be null
• Input array cannot be null or empty.

AI-assisted analysis of TheAlgorithms/Java@fdfb9a395b (2026-08-13). Data as JSON: /api/errors/543ac28d19c997e2. Report an issue: GitHub.