The Bug:

Igloos can generate without basements but with trapdoors leading to basements.

It's important to note that this report is not about the igloo generating in mid-air; that problem is being tracked on MC-91084. This report (MC-238539) is about igloos have generating without a basement but with a trapdoor. In other words, if a basement isn't generated, there shouldn't be a trapdoor leading to a non-existent basement.

Here is an example:

Seed: 1359968930092793278
Coordinates: /execute in minecraft:overworld run tp @s 43715.33 64.00 4650.07 -180.93 -49.95

Steps to Reproduce:

1. Generate a world with the seed provided above and teleport to the given coordinates.
2. Look closely at how the igloo has generated.
3. Take note as to whether or not igloos can generate without basements but with trapdoors leading to basements.

Observed Behavior:

Igloos can generate without basements but with trapdoors leading to basements.

Expected Behavior:

Igloos would not be able to generate without basements when there are trapdoors leading to basements within the structure.