public Builder fromExecConfig(ConfigSource configSource) {
            final Optional<Instant> transactionTime =
                    toInstantFromString(configSource.get(String.class, "transaction_time", null));
            if (transactionTime.isPresent()) {
                this.transactionTime = transactionTime.get();
            }
            return this;
        }
Provides access inside Embulk through a transactional session.

<p>It is internal implementation of {@link ExecSession} although some methods, such as {@code newPlugin}, are to be
removed from {@link ExecSession} soon during Embulk v0.10 when {@link ExecSession} moves to {@code embulk-spi} from
{@code embulk-core}. Even after the removal, they stay in this {@link ExecSessionInternal} to be called through
{@link ExecInternal}.
embulk-core/src/main/java/org/embulk/spi/ExecSessionInternal.java