`onChainCheck` crashes when chain metadata lacks an RPC endpoint

[MrLightspeed]

Summary

If a contributor adds a new chain to networkMapping before the ethereum-lists/chains dataset includes that chain, ./gradlew onChainCheck throws a NoSuchElementException instead of skipping the on-chain validation.

Steps to reproduce

1. Checkout master at e0794ee`.
2. Extend networkMapping with a placeholder entry, e.g. add "demo" to 4242424242.
3. Create tokens/demo/0x0000000000000000000000000000000000000001.json with valid metadata.
4. Run export JAVA_HOME=$HOME/.jdks/jdk-17.0.13+11 && export PATH=$JAVA_HOME/bin:$PATH.
5. Run ./gradlew onChainCheck -PfileToCheck=tokens/demo/0x0000000000000000000000000000000000000001.json.

Actual result

checking tokens/demo/0x0000000000000000000000000000000000000001.jsonException in thread "main" 
java.util.NoSuchElementException: Collection contains no element matching the predicate.
    at org.ethereum.lists.tokens.TokenCheckerKt.getRPC-B0vcT2Q(TokenChecker.kt:198)
    at org.ethereum.lists.tokens.TokenCheckerKt.checkTokenFile-StX6v-4(TokenChecker.kt:100)
    …

The task aborts instead of continuing with pure JSON validation.

Expected result

If no RPC endpoint exists for the chain yet, we should emit a warning and skip the RPC checks, letting the remainder of the validations finish successfully.

Environment

• Commit: e0794ee
• JDK: openjdk version "17.0.13" 2024-10-15 (Temurin-17.0.13+11)
• OS: Ubuntu 22.04 (WSL)

Related PR

• fix: handle missing RPC endpoints for new chains #978 makes getRPC resilient by using firstOrNull and returning null when no RPC exists, so onChainCheck can proceed with a descriptive warning instead of crashing.