Fixed #130

release-notes/VERSION-2.x

@@ -11,6 +11,8 @@ Modules:
 2.12.0 (not yet released)
 
 #71: (yaml) Hex number as an entry of an Object causing problem(s) with binding to POJO
+#130: (yaml) Empty String deserialized as `null` instead of empty string
+ (reported by iulianrosca@github)
 #175: (yaml) Add `YAMLGenerator.Feature.INDENT_ARRAYS_WITH_INDICATOR` to indent by 2 spaces
  (requested by Jesper N; fix contributed by Damian S)
 #199: (csv) Empty Lists can only be String-typed in CSV

yaml/src/main/java/com/fasterxml/jackson/dataformat/yaml/YAMLMapper.java

@@ -31,8 +31,30 @@ public Builder(YAMLMapper m) {
         /******************************************************************
          */
 
-        // No Parser-features yet
-
+        public Builder enable(YAMLParser.Feature... features) {
+            for (YAMLParser.Feature f : features) {
+                _mapper.enable(f);
+            }
+            return this;
+        }
+
+        public Builder disable(YAMLParser.Feature... features) {
+            for (YAMLParser.Feature f : features) {
+                _mapper.disable(f);
+            }
+            return this;
+        }
+
+        public Builder configure(YAMLParser.Feature f, boolean state)
+        {
+            if (state) {
+                _mapper.enable(f);
+            } else {
+                _mapper.disable(f);
+            }
+            return this;
+        }
+
         public Builder enable(YAMLGenerator.Feature... features) {
             for (YAMLGenerator.Feature f : features) {
                 _mapper.enable(f);
@@ -71,7 +93,6 @@ public YAMLMapper(YAMLMapper base) {
         super(base);
     }
 
-    @SuppressWarnings("unchecked")
     public static YAMLMapper.Builder builder() {
         return new YAMLMapper.Builder(new YAMLMapper());
     }

yaml/src/main/java/com/fasterxml/jackson/dataformat/yaml/YAMLParser.java

@@ -30,6 +30,15 @@ public class YAMLParser extends ParserBase
      */
     public enum Feature implements FormatFeature // in 2.9
     {
+        /**
+         * Feature that determines whether an empty {@link String} will be parsed
+         * as {@code null}. Logic is part of YAML 1.1 
+         * <a href="https://yaml.org/type/null.html">Null Language-Independent Type</a>.
+         *<p>
+         * Feature is enabled by default in Jackson 2.12 for backwards-compatibility
+         * reasons.
+         */
+        EMPTY_STRING_AS_NULL(true)
         ;
 
         final boolean _defaultState;
@@ -84,6 +93,9 @@ private Feature(boolean defaultState) {
 
     protected int _formatFeatures;
 
+    // @since 2.12
+    protected boolean _cfgEmptyStringsToNull;
+
     /*
     /**********************************************************************
     /* Input sources
@@ -164,9 +176,9 @@ public YAMLParser(IOContext ctxt, BufferRecycler br,
         _formatFeatures = formatFeatures;
         _reader = reader;
         _yamlParser = new ParserImpl(new StreamReader(reader));
+        _cfgEmptyStringsToNull = Feature.EMPTY_STRING_AS_NULL.enabledIn(formatFeatures);
     }
 
-
     @Override
     public ObjectCodec getCodec() {
         return _objectCodec;
@@ -260,11 +272,11 @@ protected void _closeInput() throws IOException {
             _reader.close();
         }
     }
-    
+
     /*
-    /**********************************************************                              
+    /**********************************************************
     /* FormatFeature support
-    /**********************************************************                              
+    /**********************************************************
      */
 
     @Override
@@ -275,6 +287,7 @@ public int getFormatFeatures() {
     @Override
     public JsonParser overrideFormatFeatures(int values, int mask) {
         _formatFeatures = (_formatFeatures & ~mask) | (values & mask);
+        _cfgEmptyStringsToNull = Feature.EMPTY_STRING_AS_NULL.enabledIn(_formatFeatures);
         return this;
     }
 
@@ -291,6 +304,7 @@ public JsonParser overrideFormatFeatures(int values, int mask) {
     public JsonParser enable(YAMLParser.Feature f)
     {
         _formatFeatures |= f.getMask();
+        _cfgEmptyStringsToNull = Feature.EMPTY_STRING_AS_NULL.enabledIn(_formatFeatures);
         return this;
     }
 
@@ -301,6 +315,7 @@ public JsonParser enable(YAMLParser.Feature f)
     public JsonParser disable(YAMLParser.Feature f)
     {
         _formatFeatures &= ~f.getMask();
+        _cfgEmptyStringsToNull = Feature.EMPTY_STRING_AS_NULL.enabledIn(_formatFeatures);
         return this;
     }
 
@@ -520,13 +535,11 @@ protected JsonToken _decodeScalar(ScalarEvent scalar) throws IOException
         _textValue = value;
         _cleanedTextValue = null;
 
-        // [dataformats-text#130]: uncomment for 2.13 either as-is, or
-        // behind a new feature
-        /*
-        if (value.isEmpty()) {
+        // [dataformats-text#130]: Allow determining whether empty String is
+        // coerced into null or not
+        if (!_cfgEmptyStringsToNull && value.isEmpty()) {
             return JsonToken.VALUE_STRING;
         }
-        */
 
         // we may get an explicit tag, if so, use for corroborating...
         String typeTag = scalar.getTag();

yaml/src/test/java/com/fasterxml/jackson/dataformat/yaml/failing/NullFromEmptyString130Test.java

@@ -1,7 +1,8 @@
 package com.fasterxml.jackson.dataformat.yaml.failing;
 
-import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.dataformat.yaml.ModuleTestBase;
+import com.fasterxml.jackson.dataformat.yaml.YAMLMapper;
+import com.fasterxml.jackson.dataformat.yaml.YAMLParser;
 
 // [dataformats-text#130]: Easy enough to fix, if we choose to,
 //  but due to timing cannot include in 2.12 (too close to release
@@ -19,13 +20,28 @@ public void setValue(String str) {
         }
     }
 
-    private final ObjectMapper MAPPER = newObjectMapper();
+    private final YAMLMapper MAPPER = newObjectMapper();
 
     // [dataformats-text#130]
     public void testEmptyValueToNull130() throws Exception
     {
-        Value130 v = MAPPER.readerFor(Value130.class)
+        // by default, empy Strings are coerced:
+        assertTrue(MAPPER.getFactory().isEnabled(YAMLParser.Feature.EMPTY_STRING_AS_NULL));
+
+        {
+            Value130 v = MAPPER.readValue("value:   \n", Value130.class);
+            assertNull(v.value);
+            v = MAPPER.readerFor(Value130.class)
+                    .readValue("value:   \n");
+            assertNull(v.value);
+        }
+
+        // but can change that:
+        {
+            Value130 v = MAPPER.readerFor(Value130.class)
+                .without(YAMLParser.Feature.EMPTY_STRING_AS_NULL)
                 .readValue("value:   \n");
-        assertEquals("", v.value);
+            assertEquals("", v.value);
+        }
     }
 }