Fix: CompareTo when discriminatorString is null

- Fix for regression introduced by #2646 in version  13.3.1
- Replaces PR #2664

ebean-core/src/test/java/io/ebeaninternal/server/deploy/parse/DeployInheritInfoTest.java

@@ -0,0 +1,21 @@
+package io.ebeaninternal.server.deploy.parse;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class DeployInheritInfoTest {
+
+  @Test
+  void addChild_when_DiscriminatorValueIsNull() {
+    DeployInheritInfo root = new DeployInheritInfo(Object.class);
+    root.addChild(new DeployInheritInfo(Integer.class)); // DiscriminatorValue is null
+    root.addChild(new DeployInheritInfo(Short.class)); // DiscriminatorValue is null
+
+    DeployInheritInfo c2 = new DeployInheritInfo(Long.class);
+    c2.setDiscriminatorValue("c2");
+    root.addChild(c2);
+
+    assertThat(root.children()).hasSize(3);
+  }
+}