Fix test

Signed-off-by: Rishabh Maurya <rishabhmaurya05@gmail.com>

Author: rishabhmaurya

server/src/main/java/org/opensearch/index/mapper/DerivedField.java

@@ -18,6 +18,7 @@
 import org.opensearch.script.Script;
 
 import java.io.IOException;
+import java.util.Objects;
 
 /**
  * DerivedField representation: expects a name, type and script.
@@ -69,4 +70,23 @@ public Script getScript() {
         return script;
     }
 
+    @Override
+    public int hashCode() {
+        return Objects.hash(name, type, script);
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (obj == null) {
+            return false;
+        }
+        if (getClass() != obj.getClass()) {
+            return false;
+        }
+        DerivedField other = (DerivedField) obj;
+        return Objects.equals(name, other.name)
+            && Objects.equals(type, other.type)
+            && Objects.equals(script, other.script);
+    }
+
 }

server/src/main/java/org/opensearch/index/mapper/DerivedFieldMapper.java

@@ -39,7 +39,7 @@ private static DerivedFieldMapper toType(FieldMapper in) {
      */
     public static class Builder extends ParametrizedFieldMapper.Builder {
         // TODO: The type of parameter may change here if the actual underlying FieldType object is needed
-        private final Parameter<String> type = Parameter.stringParam("type", false, m -> toType(m).type, "keyword");
+        private final Parameter<String> type = Parameter.stringParam("type", false, m -> toType(m).type, "");
 
         private final Parameter<Script> script = new Parameter<>(
             "script",