fix: nil curr var

[kehiy]

Description

I added an if statement to check the value of curr to make sure it doesn't panic.

Related issues

• Fixes Seg fault / panic syncing mainnet on v1.7.4 #2134

[codecov]

Codecov Report

Patch coverage: 75.00% and project coverage change: -0.02 ⚠️

Comparison is base (a72fd91) 55.23% compared to head (986c11f) 55.22%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2152      +/-   ##
==========================================
- Coverage   55.23%   55.22%   -0.02%     
==========================================
  Files         675      675              
  Lines      113729   113731       +2     
==========================================
- Hits        62819    62808      -11     
- Misses      47066    47078      +12     
- Partials     3844     3845       +1     

Impacted Files	Coverage Δ
miner/block.go	52.52% <75.00%> (-0.02%)	⬇️

... and 22 files with indirect coverage changes

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[karlb]

The situation is still to unclear for me to trust that this change fixes the situation:

• I still don't know how the panic in Seg fault / panic syncing mainnet on v1.7.4 #2134 really happened
• We don't have a test to reproduce the issue or to test the nil case that is handled in this PR
• I suspect that returning nil from toCeloFn will cause problems for the caller, as no nil was returned before. We also still lose the error returned from GetCurrency.

[kehiy]

The situation is still too unclear for me to trust that this change fixes the situation:

• I still don't know how the panic in Seg fault / panic syncing mainnet on v1.7.4 #2134 really happened
• We don't have a test to reproduce the issue or to test the nil case that is handled in this PR
• I suspect that returning nil from toCeloFn will cause problems for the caller, as no nil was returned before. We also still lose the error returned from GetCurrency.

when we return a nil, we can make sure that the full node was not panicking.

[karlb]

when we return a nil, we can make sure that the full node was not panicking.

Have you tested what happens when nil gets returned? Maybe it just panics higher up the stack?

If it does not panic, how does returning nil affect the transactions getting executed? Will transactions with a certain feeCurrency be free, will they revert, or does something else happen?

[kehiy]

Have you tested what happens when nil gets returned? Maybe it just panics higher up the stack?

If it does not panic, how does returning nil affect the transactions getting executed? Will transactions with a certain fee currency be free, will they revert, or does something else happen?

when we return nil, if we have an error handling in higher layers it don,t panic or something else
but without error handling in higher layers we going to panic again or face with new issues.
this change just helps us to make sure the createConversionFunctions function will not panic and simply assign the issue to higher layers with error handling.