Fix NPE in FileItem compatibility layer (#651)

Author: basil

core/src/main/java/org/apache/commons/fileupload/FileItem.java

@@ -26,6 +26,7 @@
 import java.io.UnsupportedEncodingException;
 import java.nio.charset.Charset;
 import java.nio.file.Path;
+import java.util.Objects;
 import org.apache.commons.fileupload2.core.FileItemHeadersProvider;
 
 /**
@@ -331,6 +332,7 @@ public org.apache.commons.fileupload2.core.FileItem write(Path file) throws IOEx
     }
 
     static FileItem fromFileUpload2FileItem(org.apache.commons.fileupload2.core.FileItem from) {
+        Objects.requireNonNull(from);
         return new FileItem() {
 
             @Override

core/src/main/java/org/kohsuke/stapler/RequestImpl.java

@@ -1320,7 +1320,8 @@ public FileItem getFileItem2(String name) throws ServletException, IOException {
     @Deprecated
     @Override
     public org.apache.commons.fileupload.FileItem getFileItem(String name) throws ServletException, IOException {
-        return org.apache.commons.fileupload.FileItem.fromFileUpload2FileItem(getFileItem2(name));
+        FileItem fileItem = getFileItem2(name);
+        return fileItem != null ? org.apache.commons.fileupload.FileItem.fromFileUpload2FileItem(fileItem) : null;
     }
 
     private static final Logger LOGGER = Logger.getLogger(RequestImpl.class.getName());