Allow overriding (with unsetting) in config files

Author: ianfixes

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Fixed
 - Spaces in the names of project directores no longer cause unit test binaries to fail execution
+- Configuration file overrides with `nil`s (or empty arrays) now properly override their base configuration
 
 ### Security
 

lib/arduino_ci/ci_config.rb

@@ -93,7 +93,7 @@ def validate_data(rootname, source, schema)
         if !schema.include?(ksym)
           puts "Warning: unknown field '#{ksym}' under definition for #{rootname}"
         elsif value.nil?
-          # unspecificed, that's fine
+          good_data[ksym] = nil
         elsif value.class != expected_type
           puts "Warning: expected field '#{ksym}' of #{rootname} to be '#{expected_type}', got '#{value.class}'"
         else