leading space was removed and hard to combine java stacktrace

[fengxx]

looks like splunk-otel-collector removes leading space by default, it is hard to combine java stacktrace

Exception in thread "main" java.lang.NullPointerException
        at com.example.myproject.Book.getTitle(Book.java:16)
        at com.example.myproject.Author.getBookTitles(Author.java:25)
        at com.example.myproject.Bootstrap.main(Bootstrap.java:14)

recombine expected to work for checking leading space :

      include:
        - /path-to-logs/*.log
      start_at: beginning
      operators:
        - type: recombine
          combine_field: body
          is_first_entry: body matches "^[^ ]+"

has to use an urgly workaround

is_first_entry: not (body startsWith "at " )