app-help and app-exit gives an error when entering it as the first command

[halfwhole]

How to reproduce:

• Start the app.
• Enter as the first command app-help or app-exit.

Result:

• Error: Command attempted to make changes but is not a MutatorCommand

It works on subsequent tries though, but not the first one.

[EDIT: this probably works on many/all commands here on my side, so changing the severity to High.]

[nus-pe-bot]

Team's Response

Accepted.

The bug only happens:

1. When the app is first started up
2. On the first command
3. When that first command is a non-data-modifying command

As this is a very specific scenario (and the user will be able to continue using the application after the initial error; all subsequent command execute properly), the severity it set at medium.

This bug happens because some code attempts to sort the staged appointment book upon startup, resulting in the staged appointment book being different from the base appointment book. If a non-data-modifying command is executed as the first command, the change (sorting) is attributed to that command, and the app defensively prevents the change by reverting the staged appointments to the base appointments and producing the error message.

The bug can be fixed by modifying the code at this location: https://github.com/AY1920S1-CS2103-F10-1/main/blob/569608fee9380a1f1cdcb455bbf0af88a4f253c3/src/main/java/cs/f10/t1/nursetraverse/model/ModelManager.java#L93

Items for the Tester to Verify

❓ Issue severity

Team chose [severity.Medium].
Originally [severity.High].

• I disagree

Reason for disagreement: [replace this with your reason]

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