Rename field IsValidated in mri_upload table

[MounaSafiHarab]

to IsCandidateInfoValidated, and set its default to NULL
This is related to pull request: aces/Loris-MRI#106
in LORIS-MRI

[codecov-io]

Current coverage is 24.65%

Merging #1501 into 16.04-dev will increase coverage by +0.73% as of 181708b

@@            16.04-dev   #1501   diff @@
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  Files             110     110       
  Stmts           18444   18446     +2
  Branches            0       0       
  Methods          1024    1024       
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+ Hit              4413    4547   +134
  Partial             0       0       
+ Missed          14031   13899   -132

Review entire Coverage Diff as of 181708b

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[driusan]

Why the change in default from false to null? I can't think of any reasons this flag would need to be null and false seems like a reasonable default..

[MounaSafiHarab]

To discern between the 3 cases (This is in reference to redmine task#7678):

1. Preprocessing is run from the imaging_upload_file.pl step, which then gives two outputs: 1 if IsValidated is true and 0 if false. This validation only takes place if preprocessing happens using imaging_upload_file.pl (which does not take place if we run the preprocessing using option 2) below).
2. Preprocessing is run from the tarchiveLoader step, in which case, the IsValidated should be set to default, or NULL (as opposed to 0).

[driusan]

Is the reasoning is that there's 3 values, I'm not sure that having "null" be treated as a special magic value is the right way to go, because you need to memorize the difference between false and null. Maybe it should be a non-null enum (CandidateInfoValidityStatus?) with a default of something like 'Unknown'?