Better handling of misconfiguration / missing types.

[bvarner]

As explained by rbartl in issue #7

got that Unexpected Throwable: java.lang.NullPointerException error in my fresh setup. After some added debugging i found it was a missing java_memory line in the types.db file.

types.db java_memory value:GAUGE:0:U a null pointer exception in the config method was preventing the executor field to be set. A try catch block around the whole config block to see these config errors would be a good idea.