Error when opening the "Variables" category in Blockly

[T94T]

Attempting to open/clicking the "Variables" category results in an error, and no blocks are displayed.

• Error in official demo ("Blockly -> Demos -> Code"): Uncaught TypeError: c is undefined in blockly_compressed.js.
• Error in my custom project (using the current branch with last commit bde0047): Uncaught TypeError: Cannot read properties of undefined (reading 'length') in blockly_compressed.js.