During the general session at CFUN04 this weekend, a ColdFusion user asked a question regarding why "null null" error messages occur in ColdFusion MX. This is bug 51579 and the problem occurs when CFERROR is used for custom exception handling and a Null Pointer Exception occurs at runtime. This causes the cferror variable error.diagnostics to be populated with the value of "null null". Normally, error.diagnostics is the concatenation of cfcatch.message and cfcatch.detail, but during an NPE they each evaluate to null when cferror is used and so the result is "null null". If you know of any other way to generate this rather unhelpful error message and you have a small, exact reproducible case, then please let me know.

Update: This bug has a hotfix for CFMX 6.1 and CFMX 6.1 Updater 1:

Hot fix for null, null errors