null elements are not indexed. Lucene does not support null elements and this does not make much sense either.

String are indexed as is

Numbers are converted in their String representation. Note that numbers cannot be compared by Lucene (ie used in ranged queries) out of the box: they have to be padded ^[1]

Dates are stored as yyyyMMddHHmmssSSS in GMT time (200611072203012 for Nov 7th of 2006 4:03PM and 12ms EST). You shouldn't really bother with the internal format. What is important is that when using a DateRange Query, you should know that the dates have to be expressed in GMT time.

Usually, storing the date up to the milisecond is not necessary. @DateBridge defines the appropriate resolution you are willing to store in the index (@DateBridge(resolution=Resolution.DAY)). The date pattern will then be truncated accordingly.

@Entity @Indexed 
public class Meeting {
    @Field(index=Index.UN_TOKENIZED)
    @DateBridge(resolution=Resolution.MINUTE)
    private Date date;
    ...
}