Buffer.Reserve Wrong Condition?

[SamanKia]

Hi.
I don't get first line in your reserve method? is this a type or I miss something?
Debug.Assert((capacity >= 0), "Invalid reserve capacity!");

/// <summary>
/// Reserve the buffer of the given capacity
/// </summary>
public void Reserve(long capacity)
{
    Debug.Assert((capacity >= 0), "Invalid reserve capacity!");
    if (capacity < 0)
        throw new ArgumentException("Invalid reserve capacity!", nameof(capacity));

    if (capacity > Capacity)
    {
        byte[] data = new byte[Math.Max(capacity, 2 * Capacity)];
        Array.Copy(_data, 0, data, 0, _size);
        _data = data;
    }
}

[chronoxor]

https://stackoverflow.com/questions/129120/when-should-i-use-debug-assert