[Gimp-developer] Invalid input arguments of file-raw-save2

I'm trying to write my own scripts to save a selection to a RAW file with GIMP script-fu.
I found that the argument "image-type" in "file-raw-save2" expects values from { RAW_RGB (0), RAW_PLANAR (3) }. When using 3 for this argument, I got the following result:
        Error: Procedure execution of file-raw-save2 failed on invalid input arguments.
However 0 is OK for "image-type" and the image is saved successfully.
Does anyone know how to fix this?

Here is some information about my system:
GIMP version: 2.10.14
Operating System: Windows 10 professional v1809

Reproduction
1. Save following content as a .scm file in gimp’s script folder. (The mentioned file-raw-save2 function is in line 89.)
--------------------------------------------------------------------------------------
(define (split-path path)
    (let*
        (
            (ret '())
        )
		(for-each
			(lambda (part)
				(set! ret (append ret (strbreakup part DIR-SEPARATOR)))
			)
			(strbreakup path DIR-SEPARATOR)
		)
		ret
	)
)


(define (script-fu-compose-file-name inImage
                                    inRowIndex
                                    inColumnIndex
                                    inWidth
                                    inHeight)
    (let*
        (
            (fileName "")
            (filePath (car (gimp-image-get-filename inImage)))
            (fileDir (unbreakupstr (butlast (split-path filePath)) DIR-SEPARATOR))
        )
        (set! fileName
            (string-append
                fileDir
                DIR-SEPARATOR
                (number->string inRowIndex)
                "_"
                (number->string inColumnIndex)
                "_"
                (number->string inWidth)
                "_"
                (number->string inHeight)
                ".xcf"
            )
        )
        fileName
    )
)

(define (script-fu-save-selection inImage
                                inDrawable
                                inRowIndex
                                inColumnIndex
                                inX
                                inY
                                inChunkLength
                                inImageWidth
                                inImageHeight)
    (let*
        (
            (theWidth 0)
            (theWitdhExpected 0)
            (theHeight 0)
            (theHeightExpected 0)
            (theRAWDefaults (file-raw-get-defaults))
        )
        (file-raw-set-defaults 3 0)
        (set! theWitdhExpected (- (+ inX inChunkLength) 1))
        (if (<= theWitdhExpected inImageWidth)
            (set! theWidth inChunkLength)
            (set! theWidth (- inImageWidth inX))
        )

        (set! theHeightExpected (- (+ inY inChunkLength) 1))
        (if (<= theHeightExpected inImageHeight)
            (set! theHeight inChunkLength)
            (set! theHeight (- inImageHeight inY))
        )
        (gimp-image-select-rectangle inImage CHANNEL-OP-REPLACE inX inY theWidth theHeight)
        (gimp-edit-copy inDrawable)
        (let*
            (
                (theFileName (script-fu-compose-file-name inImage inRowIndex inColumnIndex theWidth theHeight))
                (theNewImage (car (gimp-edit-paste-as-new-image)))
                (theNewDrawable 0)
            )
            (set! theNewDrawable (car (gimp-image-get-active-drawable theNewImage)))
;            (gimp-file-save RUN-NONINTERACTIVE
;                            theNewImage
;                            theNewDrawable
;                            theFileName
;                            theFileName)
            (file-raw-save2 RUN-NONINTERACTIVE
                            theNewImage
                            theNewDrawable
                            theFileName
                            theFileName
                            3
                            0)
            (gimp-image-delete theNewImage)
        )
        (file-raw-set-defaults (car theRAWDefaults) (cadr theRAWDefaults))
    )
)

(define (script-fu-split-image inImage
                            inDrawable
                            inXPos
                            inYPos
                            inChunkLength
                            )
    (let*
        (
            (theRowCount 0)
            (theColumnCount 0)
            (theImageWidth 0)
            (theImageHeight 0)
            (theRowIndex 0)
            (theColumnIndex 0)
            (theX 0)
            (theY 0)
        )
        (set! theImageWidth (car (gimp-image-width inImage)))
        (set! theImageHeight (car (gimp-image-height inImage)))
        (set! theRowCount (/ theImageHeight (- inChunkLength 1)))
        (set! theColumnCount (/ theImageWidth (- inChunkLength 1)))
        (while (<= theRowIndex theRowCount)
            (set! theY (+ (* theRowIndex (- inChunkLength 1)) inYPos))
            (if (< theY (- theImageHeight 1))
                (begin
                    (set! theColumnIndex 0)
                    (while (<= theColumnIndex theColumnCount)
                        (set! theX (+ (* theColumnIndex (- inChunkLength 1)) inXPos))
                        (if (< theX (- theImageWidth 1))
                            (script-fu-save-selection inImage
                                                    inDrawable
                                                    theRowIndex
                                                    theColumnIndex
                                                    theX
                                                    theY
                                                    inChunkLength
                                                    theImageWidth
                                                    theImageHeight)
                        )
                        (set! theColumnIndex (+ theColumnIndex 1))
                    )
                )
            )
            (set! theRowIndex (+ theRowIndex 1))
        )
    )
)

(script-fu-register
    "script-fu-split-image"                      ;func name
    "Split Image"                                ;menu label
    "Split image at top left point with length." ;description
    "XXXXXX"                                     ;author
    "copyright XXX, 2019, XXXXXX"                ;copyright notice
    "December 28, 2019"                          ;date created
    "RGB* GRAY*"                                 ;image type that the script works on
  SF-IMAGE       "Image to Split"    0
  SF-DRAWABLE    "Drawable to Split" 0
  SF-VALUE       _"X Position"       "0"
  SF-VALUE       _"Y Position"       "0"
  SF-VALUE       _"Chunk Length"     "513"
)

(script-fu-menu-register "script-fu-split-image"
                         "<Image>/Filters/Web")
---------------------------------------------------------------------------------------
2. Open an image with GIMP.
3. Select from menu “Filters” -> “Web” -> “Split Image”.
4. Click the OK button on the dialog, and you can find the error message from GIMP’s Error Console:
Split Image Warning
Error while executing script-fu-split-image:
Error: Procedure execution of file-raw-save2 failed on invalid input arguments.
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