Export feature does not work consistently

[nus-pe-script]

Describe the bug
Export command gives the 'Export failed!' error, when example command is given.

To Reproduce
Steps to reproduce the behavior:

1. Type 'export 2 csv' in the Command Line and press 'Enter'
2. See error 'Export failed!'

Expected behavior
Contact details of person with INDEX 2 is exported in csv format.

Screenshots

Additional context
This command works on other occasions.

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Reported by: @darylnigel
Severity: Medium

_{[original: nusCS2113-AY1819S1/pe-1#421]}

[elstonayx]

feature is removed and replaced with another feature in #200