public static String localDateTimeToString(LocalDateTime value, String emptyTimeString) {
        return (value == null) ? emptyTimeString : value.toString();
    }
public static String localDateTimeToString ( LocalDateTime value , String emptyTimeString ) { return ( value == null ) ? emptyTimeString : value . toString ( ) ; }
localDateTimeToString, This will return the supplied LocalDateTime as a string. If the value
is null, this will return the value of emptyTimeString. Time values will be output in the
same format as LocalDateTime.toString().

Javadocs from LocalDateTime.toString():

Outputs this date-time as a {@code String}, such as {@code 2007-12-03T10:15:30}.
<p>
The output will be one of the following ISO-8601 formats:
<ul>
<li>{@code uuuu-MM-dd'T'HH:mm}</li>
<li>{@code uuuu-MM-dd'T'HH:mm:ss}</li>
<li>{@code uuuu-MM-dd'T'HH:mm:ss.SSS}</li>
<li>{@code uuuu-MM-dd'T'HH:mm:ss.SSSSSS}</li>
<li>{@code uuuu-MM-dd'T'HH:mm:ss.SSSSSSSSS}</li>
</ul>
The format used will be the shortest that outputs the full value of the time where the
omitted parts are implied to be zero.