CloudWatch metric filters dimensions cannot include whitespace?

When creating dimensions from CloudWatch logs using metric filter with JSON fields, any value with a space, like "First phase" is registered as a blank dimension value. If the value has no space, like "First_phase", it is properly registered.

Dimension name, however, can be created with a space. The problem is just with dimension values.

The description in the filter creation dialog states: "Dimension names and values can be up to 255 characters, cannot contain blank spaces or non-ASCII characters". It also directs to https://docs.aws.amazon.com/AmazonCloudWatch/latest/APIReference/API_Dimension.html, which states: "The value of the dimension. Dimension values must contain only ASCII characters and must include at least one non-whitespace character."

One the one hand, the wording of the metric creation dialog warns "cannot contain blank spaces". However, the formal docs say "must include at least one non-whitespace character". The dimension name follows the formal docs, the value seems to follow the dialog's wording.

Is it a bug?