Please find the entire stack trace in your log and post that here. I tried saving without keyfile as you suggested and did not see any problem.
Why did you file this under "deploy" instead of "scp"?

Sory, I didn't see a selection for SCP in the Jira drop-down. Here are the log entries:

Mar 15, 2010 12:50:10 PM hudson.plugins.dbcharts.DbChartPublisher$DescriptorImpl configure
INFO: DescriptorImpl.configure:{}

Mar 15, 2010 12:49:26 PM hudson.plugins.dbcharts.DbChartPublisher$DescriptorImpl getJDBCConnectionDescriptors
INFO: getJDBCConnectionDescriptors(): custom=hudson.plugins.dbcharts.CustomJDBCConnection$CustomJDBCConnectionDescriptor@3316f2e6; mysql=hudson.plugins.dbcharts.MySQLJDBCConnection$MySQLJDBCConnectionDescriptor@27a4f43e

I don't see what this has to do with charts. But these two entries occur each time I get the NPE, so this has to be related. Maybe only through the return path from Configure System to Manage Hudson in the presence of graphics errors.

I am trying to display charts produced by the PMD plugin, and haven't gotten those working yet. I get the graphical error:
Graphics N/A. Unable to access X. You need to run the web container in the headless mode. Add -Djava.awt.headless=true to VM.
Even though looking in the Hudson system settings shows that's already set.

Is that it for log entries? Not sure where to look if we can't find the full stack trace for the NPE.

ok, I installed dbcharts and was able to reproduce the error (and you're right.. no full stack trace in the log). So this is a form field conflict between dbcharts and scp plugins.. gives me something to dig into.

I don't think scp plugin is involved at all. Just install dbCharts plugin and save the global config w/o adding any JDBC connections gets this error.

Code changed in hudson
User: : mindless
Path:
trunk/hudson/plugins/dbCharts/pom.xml
trunk/hudson/plugins/dbCharts/src/main/java/hudson/plugins/dbcharts/Chart.java
trunk/hudson/plugins/dbCharts/src/main/java/hudson/plugins/dbcharts/DbChartPublisher.java
trunk/hudson/plugins/dbCharts/src/main/resources/hudson/plugins/dbcharts/DbChartPublisher/config.jelly
trunk/hudson/plugins/dbCharts/src/main/resources/hudson/plugins/dbcharts/DbChartPublisher/global.jelly
trunk/hudson/plugins/dbCharts/src/main/resources/index.jelly
http://jenkins-ci.org/commit/28684
Log:
[FIXED JENKINS-5916] avoid NPE if global config is saved with no JDBC connections entered.
Also changed log output to "fine" level, removed unused help links and added plugin desc.

Thanks! Great job!