"There is no short book in my house."
Translation:لَيْسَ هُناك كِتاب قَصير في بَيْتي.
Do you think هُناك is needed in this sentence, since there is already في بَيْتي? It seems redundant, because both indicate the place whe Something is (or is not). Well, at least I wrote لَيْسَ كِتاب قَصير في بَيْتي and it was rejected.
Removing هناك would require re-arranging the sentence a bit, and abandon the use of ليس.
If I was in Duolingo's shoes I would put the sentence more like: لا يوجد كتاب قصير في بيتي (there is no short book in my house) - whatever "short book" means.
ليس في بيتي كتاب قصير
That's an acceptable alternative. Sounds a bit stilted for everyday use, but then again, all of MSA is.