JDK1.4, all platforms:

NPE thrown which stack trace points to code I think is unable to produce such exception.

See the issuezilla:
http://www.netbeans.org/issues/show_bug.cgi?id=13840

java -version:
java version "1.4.0-beta3"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.0-beta3-b78)
Java HotSpot(TM) Client VM (build 1.4.0-beta3-b78, mixed mode)
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There is a different behaviour on a Linux, Solaris system. IDE crashed with HotSpot Virtual Machine Error : 11.
I've attached an appropriate log file (Linux).
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For reproduce the bug I know only this testcase:
1. Start IDE
2. Mount a big filesystem (for example IDE's sources) in the Explorer
3. Invoke a Find action from popup menu on the appropriate filesystem
4. Fill some string into Substring and press Search