Improve exception message for invalid fallback config (#1424)

* Add specific error message

* Extend message

Author: aaronweissler

inspectit-ocelot-core/src/main/java/rocks/inspectit/ocelot/core/config/InspectitEnvironment.java

@@ -211,7 +211,12 @@ protected void configurePropertySources(Optional<String> cmdLineArgs) {
             currentSources.forEach(ps -> propsList.remove(ps.getName()));
             fallbackSources.forEach(ps -> propsList.addLast(ps));
 
-            currentConfig = loadAndValidateFromProperties(INSPECTIT_ROOT_PREFIX, InspectitConfig.class).get();
+            Optional<InspectitConfig> fallbackConfig = loadAndValidateFromProperties(INSPECTIT_ROOT_PREFIX, InspectitConfig.class);
+            if (fallbackConfig.isPresent()) {
+                currentConfig = fallbackConfig.get();
+            } else {
+                throw new RuntimeException("The fallback configuration could not be parsed, probably due to a validation error. See logs for further information.");
+            }
 
             fallbackSources.forEach(ps -> propsList.remove(ps.getName()));
             currentSources.forEach(ps -> propsList.addLast(ps));