Add failing test case for #4200.

src/test/java/com/fasterxml/jackson/failing/NullConversionsForContent4200Test.java

@@ -0,0 +1,63 @@
+package com.fasterxml.jackson.failing;
+
+import java.util.Map;
+
+import com.fasterxml.jackson.annotation.*;
+
+import com.fasterxml.jackson.databind.*;
+import com.fasterxml.jackson.databind.exc.InvalidNullException;
+
+// [databind#4200]: Nulls.FAIL not taken into account with DELEGATING creator
+public class NullConversionsForContent4200Test extends BaseMapTest
+{
+    static class DelegatingWrapper4200 {
+        private final Map<String, String> value;
+
+        @JsonCreator(mode = JsonCreator.Mode.DELEGATING)
+        DelegatingWrapper4200(@JsonSetter(contentNulls = Nulls.FAIL)
+            Map<String, String> value)
+        {
+            this.value = value;
+        }
+
+        public Map<String, String> getValue() {
+            return value;
+        }
+    }
+
+    static class SetterWrapper4200 {
+        private Map<String, String> value;
+
+        public Map<String, String> getValue() {
+            return value;
+        }
+
+        @JsonSetter(contentNulls = Nulls.FAIL)
+        public void setValue(Map<String, String> value) {
+            this.value = value;
+        }
+    }
+
+    private final ObjectMapper MAPPER = newJsonMapper();
+
+    public void testDelegatingCreatorNulls4200() throws Exception
+    {
+        try {
+            MAPPER.readValue(a2q("{'foo': null}"), DelegatingWrapper4200.class);
+            fail("Should not pass");
+        } catch (InvalidNullException e) {
+            verifyException(e, "Invalid `null` value");
+        }
+    }
+
+    public void testSetterNulls4200() throws Exception
+    {
+        try {
+            MAPPER.readValue(a2q("{'value':{'foo': null}}"),
+                    SetterWrapper4200.class);
+            fail("Should not pass");
+        } catch (InvalidNullException e) {
+            verifyException(e, "Invalid `null` value");
+        }
+    }
+}