Add more tests for #72; fix an accidental exclusion of empty String f…

…or deserialization

src/main/java/com/fasterxml/jackson/dataformat/csv/CsvParser.java

@@ -316,7 +316,7 @@ public void setSchema(FormatSchema schema)
         if (schema instanceof CsvSchema) {
             _schema = (CsvSchema) schema;
             String str = _schema.getNullValueString();
-            _nullValue = str.isEmpty() ? null : str;
+            _nullValue = str;
         } else if (schema == null) {
             schema = EMPTY_SCHEMA;
         } else {

src/main/java/com/fasterxml/jackson/dataformat/csv/CsvSchema.java

@@ -41,7 +41,7 @@
  *  </li>
  * <li>nullValue (String) [default: "" (empty String)]: When asked to write Java `null`,
  *    this String value will be used instead.<br />
- *   NOTE: NOT used for reading at this point (this may change in future)
+ *   With 2.6, value will also be recognized during value reads.
  *  </li>
  * </ul>
  *<p>
@@ -545,7 +545,7 @@ public Builder setLineSeparator(char lf) {
         }
 
         public Builder setNullValue(String nvl) {
-            return setNullValue(nvl.toCharArray());
+            return setNullValue((nvl == null) ? null : nvl.toCharArray());
         }
 
         public Builder setNullValue(char[] nvl) {

src/test/java/com/fasterxml/jackson/dataformat/csv/deser/NullReadTest.java

@@ -0,0 +1,98 @@
+package com.fasterxml.jackson.dataformat.csv.deser;
+
+import com.fasterxml.jackson.databind.*;
+import com.fasterxml.jackson.dataformat.csv.*;
+
+public class NullReadTest extends ModuleTestBase
+{
+    final CsvMapper MAPPER = mapperForCsv();
+
+    // For [dataformat-csv#72]: recognize "null value" for reading too
+    public void testReadNullValue72() throws Exception
+    {
+        CsvSchema schema = CsvSchema.builder()
+                .setNullValue("n/a")
+                .addColumn("id")
+                .addColumn("desc")
+                .build();
+
+        // start by writing, first
+        String csv = MAPPER.writer(schema).writeValueAsString(new IdDesc("id", null));
+        // MUST use doubling for quotes!
+        assertEquals("id,n/a\n", csv);
+
+        // but read back
+
+        ObjectReader r = MAPPER.readerFor(IdDesc.class)
+                .with(schema);
+
+        IdDesc result = r.readValue(csv);
+        assertNotNull(result);
+        assertEquals("id", result.id);
+        assertNull(result.desc);
+
+        // also try the other combination
+        result = r.readValue("n/a,Whatevs\n");
+        assertNotNull(result);
+        assertNull(result.id);
+        assertEquals("Whatevs", result.desc);
+    }
+
+    public void testReadNullValueFromEmptyString() throws Exception
+    {
+        // first: empty String should work as default
+        CsvSchema schemaWithDefault = CsvSchema.builder()
+                .addColumn("id")
+                .addColumn("desc")
+                .build();
+
+        // start by writing, first
+        String csv = MAPPER.writer(schemaWithDefault).writeValueAsString(new IdDesc("id", null));
+        assertEquals("id,\n", csv);
+
+        // but read back
+
+        ObjectReader r = MAPPER.readerFor(IdDesc.class).with(schemaWithDefault);
+
+        IdDesc result = r.readValue(csv);
+        assertNotNull(result);
+        assertEquals("id", result.id);
+        assertNull(result.desc);
+
+        // also try the other combination
+        result = r.readValue(",Whatevs\n");
+        assertNotNull(result);
+        assertNull(result.id);
+        assertEquals("Whatevs", result.desc);
+
+        // And then with explicit Empty String
+        CsvSchema schemaWithExplicitEmpty = CsvSchema.builder()
+                .setNullValue("")
+                .addColumn("id")
+                .addColumn("desc")
+                .build();
+
+        csv = MAPPER.writer(schemaWithExplicitEmpty).writeValueAsString(new IdDesc("id", null));
+        assertEquals("id,\n", csv);
+        r = MAPPER.readerFor(IdDesc.class).with(schemaWithExplicitEmpty);
+        result = r.readValue(csv);
+        assertNotNull(result);
+        assertEquals("id", result.id);
+        assertNull(result.desc);
+
+        // and finally with explicit `null`
+        CsvSchema schemaWithExplicitNull = CsvSchema.builder()
+                .setNullValue((String) null)
+                .addColumn("id")
+                .addColumn("desc")
+                .build();
+
+        csv = MAPPER.writer(schemaWithExplicitNull).writeValueAsString(new IdDesc("id", null));
+        assertEquals("id,\n", csv);
+        r = MAPPER.readerFor(IdDesc.class).with(schemaWithExplicitNull);
+        result = r.readValue(csv);
+        assertNotNull(result);
+        assertEquals("id", result.id);
+        assertNull(result.desc);
+    }
+}