Grok parsing fo JBOSS log of type ERROR trace

Question

This is a JBOSS Error trace , the first line is the error and the following lines containing the "at" are the description for this error:

2023-07-18 10:34:33,602 ERROR [stderr] (ServerService Thread Pool -- 82) java.io.FileNotFoundException: ./logs/log.txt (Not a directory)
2023-07-18 10:34:33,602 ERROR [stderr] (ServerService Thread Pool -- 82)    at java.io.FileOutputStream.open0(Native Method)
2023-07-18 10:34:33,602 ERROR [stderr] (ServerService Thread Pool -- 82)    at java.io.FileOutputStream.open(FileOutputStream.java:270)
2023-07-18 10:34:33,602 ERROR [stderr] (ServerService Thread Pool -- 82)    at java.io.FileOutputStream.<init>(FileOutputStream.java:213)
2023-07-18 10:34:33,602 ERROR [stderr] (ServerService Thread Pool -- 82)    at java.io.FileOutputStream.<init>(FileOutputStream.java:133)
2023-07-18 10:34:33,602 ERROR [stderr] (ServerService Thread Pool -- 82)    at org.apache.log4j.FileAppender.setFile(FileAppender.java:294)

I need to parse this bloc of lines as a one entity, the problem is that all the lines containing the "at" I want them all in one group in relation with the first line. I tried the multi-line filter but I found a problem defining the pattern.