private static Object wrapNullable(Object nullable) {
    return nullable == null ? NullT.NullValue : nullable;
  }
Wrapper objects that provide all available inputs to different parts of planetiler schema configs at runtime.
<p>
Contexts provide inputs to java code, and also global variable definitions to CEL expressions. Contexts are nested so
that all global variables from a parent context are also available to its child context.
planetiler-custommap/src/main/java/com/onthegomap/planetiler/custommap/Contexts.java