fix(log): suppress spurious error logs when solidity node exits

[317787106]

What does this PR do?

• Suppress spurious ERROR ... reason: null logs when the solidity node shuts down.

Root cause

close() calls getBlockExecutor.shutdownNow() while the get-block thread may be blocked in blockQueue.put(). That throws InterruptedException, whose getMessage() returns null. The original catch (Exception e) logged it as an ERROR with reason: null.

The original sleep() had the same issue: it caught Exception instead of InterruptedException, logged a null message, and never restored the interrupt flag.

Changes

Location	Change
getBlock()	Add catch (InterruptedException e) — restore interrupt flag, log INFO, return
getBlock()	Add !flag guard in catch (Exception e) — log INFO instead of ERROR on shutdown
getBlockByNum()	Null-check gRPC response to prevent NPE during channel teardown
getLastSolidityBlockNum()	Add !flag guard — same pattern as getBlock()
sleep()	Catch InterruptedException specifically and restore interrupt status

[halibobo1205]

Looking at DatabaseGrpcClient.getBlock(), it delegates to databaseBlockingStub.getBlockByNum(...) — a gRPC blocking stub. Per gRPC semantics, blocking stubs don't return null: success returns a response message (the default instance is still a non-null object), and channel teardown/cancellation/deadline expiry surfaces as StatusRuntimeException (CANCELLED / UNAVAILABLE / DEADLINE_EXCEEDED), not null.

A few questions:

1. Have we observed this null path being hit in production? If so, what's the server-side implementation that produces it?
2. If this is purely defensive (against mocks or future stub changes), could we add an inline comment? Future readers will spend time looking for "when does this return null."

[317787106]

You're right, it is defensive. Per gRPC semantics, a blocking stub call never returns null — on channel teardown it throws StatusRuntimeException (e.g. CANCELLED), which is already caught by the outer catch (Exception e) block and logged as INFO via the !flag guard. Removed the unreachable null check.