inheritdoc works correctly only if a closest parent has actual description (methods)

[arogachev]

Extracted from #194. Reported by @neoacevedo.

What steps will reproduce the problem?

#194 (comment)

What's expected?

Replaced description from a parent method.

What do you get instead?

Error: Call to a member function getNamespaceAliases() on null

yii2-apidoc/helpers/ApiMarkdownTrait.php

Line 149 in c13a69e

if (isset($context->phpDocContext->getNamespaceAliases()[$object])) {

Additional info

Q	A
Yii version	doesn't matter
Yii APIDoc version	master
PHP version	doesn't matter
Operating system	doesn't matter

[neoacevedo]

And it is having the same issue for closest properties:
Property $sourcePath has no parent to inherit from in neoacevedo\yii2\material\assets\MaterialAsset.. MaterialAsset inherits directly from yii\web\AssetBundle that has the $sourcePath property.