NullPointerException for list/map field access if field is null

[jaccomoc]

When accessing a field of a list or a map and the field is null we get a NullPointerException instead of a NullError which means we get an error like this:

Caused by: java.lang.NullPointerException
	at io.jactl.runtime.RuntimeUtils.loadOther(RuntimeUtils.java:1281)
	at io.jactl.runtime.RuntimeUtils.loadField(RuntimeUtils.java:1252)
	at io.jactl.pkg._$j$Script84F9187761E6A5C4CA88D78E04A6F53D._$j$main(_$j$Script84F9187761E6A5C4CA88D78E04A6F53D.jactl:72)
	at io.jactl.pkg._$j$Script84F9187761E6A5C4CA88D78E04A6F53D._$j$main$$c(_$j$Script84F9187761E6A5C4CA88D78E04A6F53D.jactl)
	at io.jactl.runtime.JactlMethodHandle.invoke(JactlMethodHandle.java:56)
	at io.jactl.runtime.Continuation.doContinue(Continuation.java:176)
	... 9 more

We should get a NullError with a better error message showing exactly where the null value is in the code.