Cater for null configuration

Author: jan

io.sloeber.autoBuild/src/io/sloeber/autoBuild/extensionPoint/providers/CommonBuilder.java

@@ -311,6 +311,8 @@ private static Set<AutoBuildConfigurationDescription> getConfigsToBuild(IProject
             cfgToBuild.add((AutoBuildConfigurationDescription) IAutoBuildConfigurationDescription
                     .getActiveConfig(project, false));
         }
+        //remove null configurations that may have been added
+        cfgToBuild.remove(null);
         return cfgToBuild;
 
     }