Bug: 500 error when submitting the cost

[zolotokrylin]

To reproduce:

1. go the the PR const reporting page
2. submit 0.15 time
3. see error (screenshot above)

[zolotokrylin]

After page refresh

[zolotokrylin]

After the second refresh

[zolotokrylin]

@georgeciubotaru getting 500 again

Let's fix it, because if I am not the only one getting it, then it might be confusing for the users (developers) and it doesn't help us.

[georgeciubotaru]

Log: investigating