Make Fields interpret null values as empty strings

jetty-core/jetty-util/src/main/java/org/eclipse/jetty/util/Fields.java

@@ -190,8 +190,9 @@ public List<String> getValuesOrEmpty(String name)
      */
     public void put(String name, String value)
     {
+        String v = value == null ? "" : value;
         // Preserve the case for the field name
-        Field field = new Field(name, value);
+        Field field = new Field(name, v);
         fields.put(name, field);
     }
 
@@ -218,13 +219,14 @@ public void put(Field field)
      */
     public void add(String name, String value)
     {
+        String v = value == null ? "" : value;
         fields.compute(name, (k, f) ->
         {
             if (f == null)
                 // Preserve the case for the field name
-                return new Field(name, value);
+                return new Field(name, v);
             else
-                return new Field(f.getName(), f.getValues(), value);
+                return new Field(f.getName(), f.getValues(), v);
         });
     }
 
@@ -246,13 +248,30 @@ public void add(String name, String... values)
             fields.compute(name, (k, f) ->
             {
                 if (f == null)
-                    return new Field(name, List.of(values));
+                    return new Field(name, toList(values));
                 else
-                    return new Field(f.getName(), f.getValues(), List.of(values));
+                    return new Field(f.getName(), f.getValues(), toList(values));
             });
         }
     }
 
+    static List<String> toList(String... strings)
+    {
+        try
+        {
+            return List.of(strings);
+        }
+        catch (NullPointerException e)
+        {
+            List<String> result = new ArrayList<>(strings.length);
+            for (String s : strings)
+            {
+                result.add(s == null ? "" : s);
+            }
+            return Collections.unmodifiableList(result);
+        }
+    }
+
     /**
      * <p>Adds the given field, storing it if none exists for the given name,
      * or adding all the values to the existing field with the given name.</p>

jetty-core/jetty-util/src/test/java/org/eclipse/jetty/util/FieldsTest.java

@@ -82,4 +82,18 @@ public void testIterator()
 
         assertThat(set, containsInAnyOrder("x", "y", "z"));
     }
+
+    @Test
+    public void testNullValues()
+    {
+        Fields fields = new Fields();
+        fields.add("x", (String)null);
+        fields.add("y", "1", null, "2");
+        fields.put("z", null);
+
+        assertThat(fields.getSize(), equalTo(3));
+        assertThat(fields.getValues("x"), contains(""));
+        assertThat(fields.getValues("y"), contains("1", "", "2"));
+        assertThat(fields.getValues("z"), contains(""));
+    }
 }