Make FieldProperty skip nulls on set() method

src/main/java/com/fasterxml/jackson/databind/deser/impl/FieldProperty.java

@@ -186,6 +186,11 @@ public Object deserializeSetAndReturn(JsonParser p,
     @Override
     public void set(Object instance, Object value) throws IOException
     {
+        if (value == null) {
+            if (_skipNulls) {
+                return;
+            }
+        }
         try {
             _field.set(instance, value);
         } catch (Exception e) {
@@ -197,6 +202,11 @@ public void set(Object instance, Object value) throws IOException
     @Override
     public Object setAndReturn(Object instance, Object value) throws IOException
     {
+        if (value == null) {
+            if (_skipNulls) {
+                return instance;
+            }
+        }
         try {
             _field.set(instance, value);
         } catch (Exception e) {

src/main/java/com/fasterxml/jackson/databind/deser/impl/MethodProperty.java

@@ -178,6 +178,11 @@ public Object deserializeSetAndReturn(JsonParser p,
     @Override
     public final void set(Object instance, Object value) throws IOException
     {
+        if (value == null) {
+            if (_skipNulls) {
+                return;
+            }
+        }
         try {
             _setter.invoke(instance, value);
         } catch (Exception e) {
@@ -189,6 +194,11 @@ public final void set(Object instance, Object value) throws IOException
     @Override
     public Object setAndReturn(Object instance, Object value) throws IOException
     {
+        if (value == null) {
+            if (_skipNulls) {
+                return instance;
+            }
+        }
         try {
             Object result = _setter.invoke(instance, value);
             return (result == null) ? instance : result;

src/test/java/com/fasterxml/jackson/databind/deser/filter/SkipNulls4441Test.java

@@ -0,0 +1,150 @@
+package com.fasterxml.jackson.databind.deser.filter;
+
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.annotation.JsonSetter;
+import com.fasterxml.jackson.annotation.Nulls;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.json.JsonMapper;
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Objects;
+
+import static com.fasterxml.jackson.databind.BaseTest.a2q;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+// [databind#4441] @JsonSetter(nulls = Nulls.SKIP) doesn't work in some situations
+public class SkipNulls4441Test {
+
+    static class Middle {
+        @JsonSetter(nulls = Nulls.SKIP)
+        private final List<Inner> listInner = new ArrayList<>();
+        private final String field1;
+
+        @JsonCreator
+        public Middle(@JsonProperty("field1") String field1) {
+            this.field1 = field1;
+        }
+
+        public List<Inner> getListInner() {
+            return listInner;
+        }
+
+        public String getField1() {
+            return field1;
+        }
+    }
+
+    static class Inner {
+        private final String field1;
+
+        @JsonCreator
+        public Inner(@JsonProperty("field1") String field1) {
+            this.field1 = field1;
+        }
+
+        public String getField1() {
+            return field1;
+        }
+    }
+
+    static class MiddleSetter {
+        private List<InnerSetter> listInner = new ArrayList<>();
+        private final String field1;
+
+        @JsonCreator
+        public MiddleSetter(@JsonProperty("field1") String field1) {
+            this.field1 = field1;
+        }
+
+        @JsonSetter(nulls = Nulls.SKIP)
+        public void setListInner(List<InnerSetter> listInner) {
+            // null passed here
+            Objects.requireNonNull(listInner);
+            this.listInner = listInner;
+        }
+
+        public List<InnerSetter> getListInner() {
+            return listInner;
+        }
+
+        public String getField1() {
+            return field1;
+        }
+    }
+
+    static class InnerSetter {
+        private final String field1;
+
+        @JsonCreator
+        public InnerSetter(@JsonProperty("field1") String field1) {
+            this.field1 = field1;
+        }
+
+        public String getField1() {
+            return field1;
+        }
+    }
+
+    private final ObjectMapper objectMapper = JsonMapper.builder().build();
+
+    private final String NULL_ENDING_JSON = a2q("{" +
+            "    'field1': 'data',     " +
+            "    'listInner': null  " +
+            "}");
+
+    private final String NULL_BEGINNING_JSON = a2q("{" +
+            "    'listInner': null,  " +
+            "    'field1': 'data'     " +
+            "}");
+
+    @Test
+    public void testFields() throws Exception {
+        // Passes
+        // For some reason, if most-inner "list1" field is null in the end, it works
+        _testFieldNullSkip(NULL_ENDING_JSON);
+        // Fails
+        // But if it's null in the beginning, it doesn't work
+        _testFieldNullSkip(NULL_BEGINNING_JSON);
+    }
+
+    @Test
+    public void testMethods() throws Exception {
+        // Passes
+        // For some reason, if most-inner "list1" field is null in the end, it works
+        _testMethodNullSkip(NULL_ENDING_JSON);
+        // Fails
+        // But if it's null in the beginning, it doesn't work
+        _testMethodNullSkip(NULL_BEGINNING_JSON);
+    }
+
+    private void _testMethodNullSkip(String s) throws Exception {
+        MiddleSetter middle = objectMapper.readValue(s, MiddleSetter.class);
+
+        testMiddleSetter(middle);
+    }
+
+    private void _testFieldNullSkip(String s) throws Exception {
+        Middle middle = objectMapper.readValue(s, Middle.class);
+
+        testMiddle(middle);
+    }
+
+    private void testMiddle(Middle middle) {
+        validateNotNull(middle);
+        validateNotNull(middle.getField1());
+        validateNotNull(middle.getListInner());
+    }
+
+    private void testMiddleSetter(MiddleSetter middle) {
+        validateNotNull(middle);
+        validateNotNull(middle.getField1());
+        validateNotNull(middle.getListInner());
+    }
+
+    private static void validateNotNull(Object o) {
+        assertNotNull(o);
+    }
+}