Accept empty string as null in PluginModel deserializer and add Coerc…

data-prepper-api/src/main/java/org/opensearch/dataprepper/model/configuration/PluginModel.java

@@ -213,8 +213,9 @@ public PluginModel deserialize(final JsonParser jsonParser, final Deserializatio
             } else if (jsonParser.currentToken() == JsonToken.VALUE_STRING) {
                 final String value = jsonParser.getValueAsString();
                 if (value.isEmpty()) {
-                    throw context.weirdStringException(value, Map.class,
-                            "Empty string is not allowed for plugin '" + pluginName + "'. Use null, empty (no value), or {} instead.");
+                    // Treat empty string same as null (YAML bare keys like "stdout:" parse as "" in Jackson 2.13+)
+                    isNull = true;
+                    jsonParser.nextToken();
                 } else {
                     throw context.weirdStringException(value, Map.class,
                             "String values not allowed for plugin '" + pluginName + "'");

data-prepper-api/src/test/java/org/opensearch/dataprepper/model/configuration/PluginModelTests.java

@@ -33,6 +33,7 @@
 
 import static org.hamcrest.CoreMatchers.equalTo;
 import static org.hamcrest.CoreMatchers.notNullValue;
+import static org.hamcrest.CoreMatchers.nullValue;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.hasKey;
@@ -229,15 +230,27 @@ final void testRoundTrip_withEmptyValue() throws IOException {
     }
 
     @Test
-    final void testDeserialize_emptyString_throwsException() throws IOException {
+    final void testDeserialize_emptyString_treatedAsNull() throws IOException {
         final InputStream inputStream = PluginModelTests.class.getResourceAsStream("plugin_model_empty_string.yaml");
         final ObjectMapper mapper = new ObjectMapper(new YAMLFactory());
 
-        final JsonMappingException exception = assertThrows(
-            JsonMappingException.class,
-            () -> mapper.readValue(inputStream, PluginModel.class)
-        );
-        assertThat(exception.getMessage(), containsString("Empty string is not allowed"));
+        final PluginModel pluginModel = mapper.readValue(inputStream, PluginModel.class);
+        assertThat(pluginModel.getPluginName(), equalTo("customPlugin"));
+        assertThat(pluginModel.getPluginSettings(), nullValue());
+    }
+
+    @Test
+    final void testDeserialize_settingsWithEmptyStringValues_preservedInMap() throws IOException {
+        final InputStream inputStream = PluginModelTests.class.getResourceAsStream("plugin_model_with_empty_string_settings.yaml");
+        final ObjectMapper mapper = new ObjectMapper(new YAMLFactory());
+
+        final PluginModel pluginModel = mapper.readValue(inputStream, PluginModel.class);
+        assertThat(pluginModel.getPluginName(), equalTo("customPlugin"));
+        assertThat(pluginModel.getPluginSettings(), notNullValue());
+        // Empty strings are preserved in the raw settings map
+        assertThat(pluginModel.getPluginSettings().get("setting_a"), equalTo(""));
+        assertThat(pluginModel.getPluginSettings().get("setting_b"), equalTo("valid_value"));
+        assertThat(pluginModel.getPluginSettings().get("setting_c"), equalTo(""));
     }
 
     @Test

data-prepper-api/src/test/java/org/opensearch/dataprepper/model/configuration/SamplePipelineConfigurationTest.java

@@ -9,7 +9,6 @@
 
 package org.opensearch.dataprepper.model.configuration;
 
-import com.fasterxml.jackson.databind.JsonMappingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.dataformat.yaml.YAMLFactory;
 import org.junit.jupiter.api.BeforeEach;
@@ -24,8 +23,6 @@
 import static org.hamcrest.CoreMatchers.equalTo;
 import static org.hamcrest.CoreMatchers.notNullValue;
 import static org.hamcrest.MatcherAssert.assertThat;
-import static org.hamcrest.Matchers.containsString;
-import static org.junit.jupiter.api.Assertions.assertThrows;
 
 /**
  * End-to-end tests for sample pipeline YAML configurations, verifying that
@@ -109,13 +106,11 @@ void deserialize_pipeline_withEmptyPluginConfig_hasEmptySettings(final String re
     }
 
     @Test
-    void deserialize_pipeline_withEmptyStringPluginConfig_throwsException() {
+    void deserialize_pipeline_withEmptyStringPluginConfig_treatedAsNull() throws IOException {
         final InputStream inputStream = getClass().getResourceAsStream("sample_pipelines/sample_pipeline_plugin_empty_string.yaml");
 
-        final JsonMappingException exception = assertThrows(
-            JsonMappingException.class,
-            () -> objectMapper.readValue(inputStream, PipelinesDataFlowModel.class)
-        );
-        assertThat(exception.getMessage(), containsString("Empty string is not allowed"));
+        final PipelinesDataFlowModel model = objectMapper.readValue(inputStream, PipelinesDataFlowModel.class);
+        assertThat(model, notNullValue());
+        assertThat(model.getPipelines().containsKey("test-pipeline"), equalTo(true));
     }
 }

data-prepper-api/src/test/resources/org/opensearch/dataprepper/model/configuration/plugin_model_with_empty_string_settings.yaml

@@ -0,0 +1,13 @@
+#
+# Copyright OpenSearch Contributors
+# SPDX-License-Identifier: Apache-2.0
+#
+# The OpenSearch Contributors require contributions made to
+# this file be licensed under the Apache-2.0 license or a
+# compatible open source license.
+#
+---
+customPlugin:
+  setting_a: ""
+  setting_b: "valid_value"
+  setting_c: ""