Missing invalid input warning in content selection

[haoyusimon]

When I was selecting the content, firstly I chose the "3. random sentence of custom length", and I have been prompted to input the custom word count (between 5 - 100). My input was 1, so I was expecting to receive an invalid input warning and still stay in the current stage of setting the custom word count. However, there was no warning, and I just entered a new round of content selection instead of staying in the setting custom word count stage. However, the warning was correctly implemented for other invalid inputs such as 1000 (refer to the screenshot).

[nus-se-script]

Your response not required for this bug as the team has accepted the bug as it is.