Fails to interpret "mydata: ~ " on write

Example :

# PDI configuration                                                                                          
pdi:
  data:
    mydata: { type: array, subtype: int, size: 2 }
  plugins:
    trace: ~
    decl_hdf5:
      file: ex_fail.h5
      write:
        mydata: ~

Outcome :

Environment loaded for PDI version 0.7.0-pre_date-2021-01-08-17_10
[PDI][NOINIT] *** Fatal error: System_error: Error while loading plugins: Config_error: Configuration error #2: Expected mapping, found scalar (ROOT){