@Override
    public String toString() {
        return MoreObjects.toStringHelper(this).omitNullValues()
                          .add("proxyType", proxyType())
                          .add("proxyAddress", proxyAddress)
                          .add("sourceAddress", sourceAddress)
                          .toString();
    }
Represents the source address. When this value is {@code null}, it will be inferred
from either the {@link ServiceRequestContext} or the local connection address.
core/src/main/java/com/linecorp/armeria/client/proxy/HAProxyConfig.java