[Linter] Robustness against nil license.

lib/cocoapods/command/spec.rb

@@ -404,14 +404,14 @@ module Pod
           messages = []
           messages << "The sources did not match any file"                     if !@spec.source_files.empty? && @pod.source_files.empty?
           messages << "The resources did not match any file"                   if !@spec.resources.empty? && @pod.resource_files.empty?
-          messages << "The preserve_paths did not match any file"              if !@spec.preserve_paths.empty? && @pod.preserve_paths.empty?
+          messages << "The preserve_paths did not match any file"              if !@spec.preserve_paths.empty? && @pod.preserve_files.empty?
           messages << "The exclude_header_search_paths did not match any file" if !@spec.exclude_header_search_paths.empty? && @pod.headers_excluded_from_search_paths.empty?
           messages
         end
 
         def file_patterns_warnings
           messages = []
-          messages << "Unable to find a license file" unless @pod.license_file || @spec.license[:type] && @spec.license[:type] == 'Public Domain'
+          messages << "Unable to find a license file" unless @pod.license_file || @spec.license && @spec.license[:type] == 'Public Domain'
           messages
         end
       end