Made InlineGet source nullable

This addresses the bug in #1042

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Signed-off-by: Brendon Faleiro <bren.faleiro@gmail.com>

java-client/src/test/java/org/opensearch/client/opensearch/_types/InlineGetTest.java

@@ -0,0 +1,68 @@
+/*
+ * 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.
+ */
+
+package org.opensearch.client.opensearch._types;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.StringReader;
+
+import org.junit.Test;
+import org.opensearch.client.json.JsonpDeserializer;
+import org.opensearch.client.json.jackson.JacksonJsonpMapper;
+import org.opensearch.client.json.jsonb.JsonbJsonpMapper;
+import org.opensearch.client.opensearch.model.ModelTestCase;
+
+import jakarta.json.stream.JsonParser;
+
+public class InlineGetTest extends ModelTestCase {
+    @Test
+    public void testInlineGet_withSource() {
+        final InlineGet inlineGet = InlineGet.of(b -> b
+            .found(true)
+            .seqNo(1L)
+            .primaryTerm(2L)
+            .routing("routing")
+            .source("{\"name\":\"John Doe\"}"));
+
+        final String jsonString = "{\"found\":true,\"_seq_no\":1,\"_primary_term\":2,\"_routing\":\"routing\","
+            + "\"_source\":\"{\\\"name\\\":\\\"John Doe\\\"}\"}";
+
+        final StringReader reader = new StringReader(jsonString);
+        final JacksonJsonpMapper mapper = new JacksonJsonpMapper();
+        final JsonParser parser = mapper.jsonProvider().createParser(reader);
+        final InlineGet actual = InlineGet.createInlineGetDeserializer(JsonpDeserializer.jsonValueDeserializer())
+            .deserialize(parser, mapper);
+        assertEquals(inlineGet.found(), actual.found());
+        assertEquals(inlineGet.seqNo(), actual.seqNo());
+        assertEquals(inlineGet.primaryTerm(), actual.primaryTerm());
+        assertEquals(inlineGet.routing(), actual.routing());
+        assertEquals(inlineGet.source(), actual.source());
+    }
+
+    @Test
+    public void testInlineGet_withoutSource() {
+        final InlineGet inlineGet = InlineGet.of(b -> b
+            .found(true)
+            .seqNo(1L)
+            .primaryTerm(2L)
+            .routing("routing"));
+
+        final String jsonString = "{\"found\":true,\"_seq_no\":1,\"_primary_term\":2,\"_routing\":\"routing\"}";
+
+        final StringReader reader = new StringReader(jsonString);
+        final JacksonJsonpMapper mapper = new JacksonJsonpMapper();
+        final JsonParser parser = mapper.jsonProvider().createParser(reader);
+        final InlineGet actual = InlineGet.createInlineGetDeserializer(JsonpDeserializer.jsonValueDeserializer())
+            .deserialize(parser, mapper);
+        assertEquals(inlineGet.found(), actual.found());
+        assertEquals(inlineGet.seqNo(), actual.seqNo());
+        assertEquals(inlineGet.primaryTerm(), actual.primaryTerm());
+        assertEquals(inlineGet.routing(), actual.routing());
+    }
+}