@Override
  public String defaultValue(final ArgSpec argSpec) {
    if (argSpec.isPositional()) {
      return null; // skip default for positional params
    }

    return envVarNames((OptionSpec) argSpec)
        .map(environment::get)
        .filter(Objects::nonNull)
        .findFirst()
        .orElse(null);
  }
Instantiates a new Environment variable default provider.

@param environment the environment
app/src/main/java/org/hyperledger/besu/cli/util/EnvironmentVariableDefaultProvider.java