Better handling of empty columns in TDF input #562
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The TDF file format cannot distinguish between string columns that contain null vs the empty string. Both are represented in the file as a zero-length string between tab delimiters. This change relates only to columns of type Text or Memo. Previously, when such a column had Required=True and AllowZeroLength=False, we would interpret a zero-length input value to be null, which would cause an exception, since Required means 'cannot be null'. This commit now assumes that in the above scenario, the zero-length input should be interpreted to mean the empty string, rather than null. If the field has AllowZeroLength=False, but no value was provided, this is an immediate error. That just leaves AllowZeroLength=True but Required=False. In this case, and for columns of all types other than Text and Memo, retain the existing behaviour, i.e. do not set the field .Value at all, and allow it to take its .DefaultValue.
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The TDF file format cannot distinguish between string columns that contain null vs the empty string. Both are represented in the file as a zero-length string between tab delimiters.
This change relates only to columns of type Text or Memo.
Previously, when such a column had Required=True and AllowZeroLength=False, we would interpret a zero-length input value to be null, which would cause an exception, since Required means 'cannot be null'.
This commit now assumes that in the above scenario, the zero-length input should be interpreted to mean the empty string, rather than null.
If the field has AllowZeroLength=False, but no value was provided, this is an immediate error.
That just leaves AllowZeroLength=True but Required=False. In this case, and for columns of all types other than Text and Memo, retain the existing behaviour, i.e. do not set the field .Value at all, and allow it to take its .DefaultValue.