Parsing "INTERVAL -'-1' YEAR"

[Hsuan Yi Chu]

Hi All,
I am trying to resolve CALCITE-922, (interval error, coming from attempting
to get value of Interval Type).

However, I found another issue regarding the "sign (i.e., + or -)" of
Interval type (see CALCITE-928). To resolve it, can somebody tell me what
this means:

"INTERVAL -'-1' YEAR"

Do the two negative signs cancel each other?