Fix Zero length check

[MikeAlhayek]

Fix #2764

[mgravell]

Comments added in #2764; there is currently insufficient context as to whether there is an error here. The syntax used is not, by itself, either correct or incorrect. It is simply syntax, and has a current meaning, which this PR changes. Whether the original code, the proposed changed code, neither, or both; are correct - is a great question, but one that neither the issue nor the PR discusses. I suggest we start there.

[mgravell]

Let's compare using:

using System;

Original(null);
Original("");
Original("abc");

Proposed(null);
Proposed("");
Proposed("abc");

static void Original(string? keyPrefix) => Write(keyPrefix?.Length == 0 ? null : keyPrefix);
static void Proposed(string? keyPrefix) => Write(keyPrefix == null || keyPrefix.Length == 0 ? null : keyPrefix);

static void Write(string? value)
    => Console.WriteLine(value is null ? "(null)" : "\"" + value + "\"");

outputs:

keyPrefix input	original output	proposed output
null	null	null
""	null	null
"abc"	"abc"	"abc"

So... this has no functional change

[mgravell]

this changes the value of IsEmpty for null values of _value; currently a null will return false for IsEmpty; with this change it will return true. The question is what should IsEmpty return for null values? IMO we should retain the current behaviour, where null reports false here (note the separate IsNull test). Changing the result of this property is a significant proposition that would require justification.

[mgravell]

Closing this; it appears to be part of a bulk creation of similar PRs on the assumption that ?.Length == 0 is automatically incorrect.