private static void putStringifiedProperty(State state, ExportEntry<?> entry, @Nullable Object value) {
        if (value != null) {
            final String valueStr = entry.stringify(value);
            if (valueStr != null) {
                state.put(entry.exportKey, valueStr);
                return;
            }
        }

        // Remove the value if it exists already.
        state.remove(entry.exportKey);
    }
Returns a {@link Map} whose key is an export key set through {@code add*()} in
{@link RequestContextExporterBuilder} and value is extracted from the specified {@link RequestContext}.
core/src/main/java/com/linecorp/armeria/common/logging/RequestContextExporter.java