Tweak Slur direction "neutral"

[Ahanu Banerjee]

When I attempt to change the "direction" property of a slur, whether that is with \tweak or \override, I cannot set the direction to neutral (0). UP (1) and DOWN (-1) work fine, but when setting to 0, I get the following error: 

"Assertion failed: d, file /home/lily/lilypond-2.24.0/release/binaries/mingw/lilypond/lilypond-2.24.0/flower/include/drul-array.hh, line 56
Exited with return code 3."

This is necessary for a function I am creating; Slur.direction has already been set to UP or DOWN earlier in the document, and I need to temporarily set it to neutral while also changing its color. (\once \slurNeutral is not practical here)

Below is example code that generates the error: 

\version "2.24"

\language "english"

{ c' d' \tweak Slur.direction #0 ( e' ) c' }

Any suggestions?

Thanks,

-Ahanu