Apply code review feedback

Signed-off-by: Oliver Lockwood <oliver.lockwood@cantab.net>

Author: oliverlockwood

client/rest/src/main/java/org/opensearch/client/Request.java

@@ -110,7 +110,13 @@ public void addParameters(Map<String, String> paramSource) {
      * will change it.
      */
     public Map<String, String> getParameters() {
-        return unmodifiableMap(parameters);
+        if (options.getParameters().isEmpty()) {
+            return unmodifiableMap(parameters);
+        } else {
+            Map<String, String> combinedParameters = new HashMap<>(parameters);
+            combinedParameters.putAll(options.getParameters());
+            return unmodifiableMap(combinedParameters);
+        }
     }
 
     /**

client/rest/src/main/java/org/opensearch/client/RequestOptions.java

@@ -91,7 +91,8 @@ public List<Header> getHeaders() {
     }
 
     /**
-     * Query parameters to attach to the request.
+     * Query parameters to attach to the request. Any parameters present here
+     * will override matching parameters in the {@link Request}, if they exist.
      */
     public Map<String, String> getParameters() {
         return parameters;
@@ -250,7 +251,8 @@ public Builder addHeader(String name, String value) {
         }
 
         /**
-         * Add the provided query parameter to the request.
+         * Add the provided query parameter to the request. Any parameters added here
+         * will override matching parameters in the {@link Request}, if they exist.
          *
          * @param name  the query parameter name
          * @param value the query parameter value

client/rest/src/main/java/org/opensearch/client/RestClient.java

@@ -832,7 +832,6 @@ private class InternalRequest {
         InternalRequest(Request request) {
             this.request = request;
             Map<String, String> params = new HashMap<>(request.getParameters());
-            params.putAll(request.getOptions().getParameters());
             // ignore is a special parameter supported by the clients, shouldn't be sent to es
             String ignoreString = params.remove("ignore");
             this.ignoreErrorCodes = getIgnoreErrorCodes(ignoreString, request.getMethod());