Fix error on clicking "Send" on an empty transfer

[csillag]

This avoids the crash on an empty amount.

Fixes #1031

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[buberdds]

I am not exactly sure what are expectations here. Do we really don't want to catch an error when a function input is invalid? Why we even trigger a submit event when a form is empty?

[csillag]

I am not exactly sure what are expectations here. Do we really don't want to catch an error when a function input is invalid? Why we even trigger a submit event when a form is empty?

The form has been implemented in such a way that when nothing is entered for the amount, it displays a "0". So it's not an invalid value, but an implicit 0.

I asked about it, and a 0 seems to be a valid value.

So I came to the conclusion that

• an empty value should mean 0
• 0 is a valid value

That's why I modified the conversion function so that we interpret "" as 0.
The other option would have been to implement this conversion at the form level, but I wanted to catch the biggest possible group of errors (ie. we might be using the same conversion function in other forms in the future), hence the implementation.

[lukaw3d]

Looks like onSubmit needs to be moved from <Button type="submit" label={t('account.sendTransaction.send', 'Send')} onClick={onSubmit} to <Form onSubmit={onSubmit}

[csillag]

Looks like onSubmit needs to be moved from <Button type="submit" label={t('account.sendTransaction.send', 'Send')} onClick={onSubmit} to <Form onSubmit={onSubmit}

OK, but then we have to adjust the fields a little bit, in order to keep the ability to submit the form without touching the amount field. (I guess we want that, since we had a "0" placeholder on the amount field. ) Done that.

[csillag]

Meanwhile, part of this has already been covered by #1070.

What remains here:

• Jest test for the error condition
• Cypress test for the error condition
• Better placeholder value for the send form (to make it obvious that an amount must be entered.)

[csillag]

Got approval from Don @donouwens about the UI/UX perspective. Technical review concluded earlier. Merging...