Arduino: cc.arduino.packages.uploaders.SerialUploader.uploadUsingProgrammer

Hello,

I have been able to upload code onto my ESP8266 for quite a long time and I think (_I think_) one of the last update broke something cause since a few days I'm getting:

Archiving built core (caching) in: /var/folders/px/5d3hxcpd2jz0j2bfvsv7mlzc0000gn/T/arduino_cache_939222/core/core_esp8266_esp8266_generic_CpuFrequency_80,ResetMethod_ck,CrystalFreq_26,FlashFreq_40,FlashMode_qio,FlashSize_512K0,led_2,LwIPVariant_v2mss536,Debug_Disabled,DebugLevel_None____,FlashErase_all,UploadSpeed_115200_ba49459f356d8c9f9eec109967582725.a
Sketch uses 263040 bytes (52%) of program storage space. Maximum is 499696 bytes.
Global variables use 33956 bytes (41%) of dynamic memory, leaving 47964 bytes for local variables. Maximum is 81920 bytes.
java.lang.NullPointerException
    at cc.arduino.packages.uploaders.SerialUploader.uploadUsingProgrammer(SerialUploader.java:314)
    at cc.arduino.packages.uploaders.SerialUploader.uploadUsingPreferences(SerialUploader.java:89)
    at cc.arduino.UploaderUtils.upload(UploaderUtils.java:78)
    at processing.app.SketchController.upload(SketchController.java:713)
    at processing.app.SketchController.exportApplet(SketchController.java:686)
    at processing.app.Editor$DefaultExportAppHandler.run(Editor.java:2265)
    at java.lang.Thread.run(Thread.java:748)

I am able to use esptool on command line to communicate with the ESP:

$ esptool.py --port /dev/cu.SLAB_USBtoUART erase_flash
esptool.py v2.2.1
Connecting....
Detecting chip type... ESP8266
Chip is ESP8266EX
Uploading stub...
Running stub...
Stub running...
Erasing flash (this may take a while)...
Chip erase completed successfully in 3.0s
Hard resetting...

Versions
Arduino IDE: 1.8.5
esp8266 board package: 2.4.1

Google has not been able to help this time :-( Any hint will be much appreciated.

Thanks in advance!