SolrRequest.getParams never null; and clarify mutability

solr/core/src/java/org/apache/solr/cli/ExportTool.java

@@ -75,8 +75,8 @@
 import org.apache.solr.common.cloud.Slice;
 import org.apache.solr.common.params.CommonParams;
 import org.apache.solr.common.params.CursorMarkParams;
-import org.apache.solr.common.params.MapSolrParams;
 import org.apache.solr.common.params.ModifiableSolrParams;
+import org.apache.solr.common.params.SolrParams;
 import org.apache.solr.common.util.CollectionUtil;
 import org.apache.solr.common.util.ExecutorUtil;
 import org.apache.solr.common.util.JavaBinCodec;
@@ -251,7 +251,7 @@ void fetchUniqueKey() throws SolrServerException, IOException {
               new GenericSolrRequest(
                       SolrRequest.METHOD.GET,
                       "/schema/uniquekey",
-                      new MapSolrParams(Collections.singletonMap("collection", coll)))
+                      SolrParams.of("collection", coll))
                   .setRequiresCollection(true));
       uniqueKey = (String) response.get("uniqueKey");
     }

solr/core/src/java/org/apache/solr/cloud/RecoveryStrategy.java

@@ -282,7 +282,6 @@ private void commitOnLeader(String leaderBaseUrl, String coreName)
       throws SolrServerException, IOException {
     try (SolrClient client = recoverySolrClientBuilder(leaderBaseUrl, coreName).build()) {
       UpdateRequest ureq = new UpdateRequest();
-      ureq.setParams(new ModifiableSolrParams());
       // ureq.getParams().set(DistributedUpdateProcessor.COMMIT_END_POINT, true);
       // ureq.getParams().set(UpdateParams.OPEN_SEARCHER, onlyLeaderIndexes);
       // Why do we need to open searcher if "onlyLeaderIndexes"?

solr/core/src/java/org/apache/solr/cloud/api/collections/CollectionHandlingUtils.java

@@ -250,7 +250,6 @@ static UpdateResponse softCommit(String baseUrl, String coreName)
             .withSocketTimeout(120000, TimeUnit.MILLISECONDS)
             .build()) {
       UpdateRequest ureq = new UpdateRequest();
-      ureq.setParams(new ModifiableSolrParams());
       ureq.setAction(AbstractUpdateRequest.ACTION.COMMIT, false, true, true);
       return ureq.process(client);
     }

solr/core/src/java/org/apache/solr/handler/ContentStreamHandlerBase.java

@@ -79,6 +79,7 @@ public void handleRequestBody(SolrQueryRequest req, SolrQueryResponse rsp) throw
     }
     try {
       SolrParams params = req.getParams();
+      assert params != null;
       UpdateRequestProcessorChain processorChain = req.getCore().getUpdateProcessorChain(params);
 
       UpdateRequestProcessor processor = processorChain.createProcessor(req, rsp);

solr/core/src/java/org/apache/solr/handler/ReplicationHandler.java

@@ -450,7 +450,7 @@ static Long getCheckSum(Checksum checksum, Path f) {
   private volatile IndexFetcher currentIndexFetcher;
 
   public IndexFetchResult doFetch(SolrParams solrParams, boolean forceReplication) {
-    String leaderUrl = solrParams == null ? null : solrParams.get(LEADER_URL, null);
+    String leaderUrl = solrParams.get(LEADER_URL, null);
     if (!indexFetchLock.tryLock()) return IndexFetchResult.LOCK_OBTAIN_FAILED;
     if (core.getCoreContainer().isShutDown()) {
       log.warn("I was asked to replicate but CoreContainer is shutting down");
@@ -1196,7 +1196,7 @@ private void setupPolling(String intervalStr) {
           try {
             log.debug("Polling for index modifications");
             markScheduledExecutionStart();
-            IndexFetchResult fetchResult = doFetch(null, false);
+            IndexFetchResult fetchResult = doFetch(SolrParams.of(), false);
             if (pollListener != null) pollListener.onComplete(core, fetchResult);
           } catch (Exception e) {
             log.error("Exception in fetching index", e);

solr/core/src/java/org/apache/solr/handler/RequestHandlerUtils.java

@@ -18,7 +18,6 @@
 
 import java.io.IOException;
 import java.util.Arrays;
-import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.Map;
@@ -53,10 +52,6 @@ public static void addExperimentalFormatWarning(SolrQueryResponse rsp) {
   public static boolean handleCommit(
       SolrQueryRequest req, UpdateRequestProcessor processor, SolrParams params, boolean force)
       throws IOException {
-    if (params == null) {
-      params = new MapSolrParams(new HashMap<>());
-    }
-
     boolean optimize = params.getBool(UpdateParams.OPTIMIZE, false);
     boolean commit = params.getBool(UpdateParams.COMMIT, false);
     boolean softCommit = params.getBool(UpdateParams.SOFT_COMMIT, false);
@@ -97,8 +92,6 @@ public static void validateCommitParams(SolrParams params) {
 
   /** Modify UpdateCommand based on request parameters */
   public static void updateCommit(CommitUpdateCommand cmd, SolrParams params) {
-    if (params == null) return;
-
     cmd.openSearcher = params.getBool(UpdateParams.OPEN_SEARCHER, cmd.openSearcher);
     cmd.waitSearcher = params.getBool(UpdateParams.WAIT_SEARCHER, cmd.waitSearcher);
     cmd.softCommit = params.getBool(UpdateParams.SOFT_COMMIT, cmd.softCommit);
@@ -114,13 +107,7 @@ public static void updateCommit(CommitUpdateCommand cmd, SolrParams params) {
   public static boolean handleRollback(
       SolrQueryRequest req, UpdateRequestProcessor processor, SolrParams params, boolean force)
       throws IOException {
-    if (params == null) {
-      params = new MapSolrParams(new HashMap<>());
-    }
-
-    boolean rollback = params.getBool(UpdateParams.ROLLBACK, false);
-
-    if (rollback || force) {
+    if (force || params.getBool(UpdateParams.ROLLBACK, false)) {
       RollbackUpdateCommand cmd = new RollbackUpdateCommand(req);
       processor.processRollback(cmd);
       return true;

solr/core/src/java/org/apache/solr/handler/UpdateRequestHandler.java

@@ -26,7 +26,6 @@
 import org.apache.solr.common.SolrException.ErrorCode;
 import org.apache.solr.common.params.CommonParams;
 import org.apache.solr.common.params.MapSolrParams;
-import org.apache.solr.common.params.ModifiableSolrParams;
 import org.apache.solr.common.params.SolrParams;
 import org.apache.solr.common.params.UpdateParams;
 import org.apache.solr.common.util.ContentStream;
@@ -124,15 +123,8 @@ public void init(NamedList<?> args) {
   }
 
   protected void setAssumeContentType(String ct) {
-    if (invariants == null) {
-      Map<String, String> map = new HashMap<>();
-      map.put(UpdateParams.ASSUME_CONTENT_TYPE, ct);
-      invariants = new MapSolrParams(map);
-    } else {
-      ModifiableSolrParams params = new ModifiableSolrParams(invariants);
-      params.set(UpdateParams.ASSUME_CONTENT_TYPE, ct);
-      invariants = params;
-    }
+    invariants =
+        SolrParams.wrapDefaults(SolrParams.of(UpdateParams.ASSUME_CONTENT_TYPE, ct), invariants);
   }
 
   private Map<String, ContentStreamLoader> pathVsLoaders = new HashMap<>();

solr/core/src/java/org/apache/solr/handler/api/V2ApiUtils.java

@@ -91,9 +91,6 @@ public static void squashIntoNamedListWithoutHeader(
   }
 
   public static String getMediaTypeFromWtParam(SolrParams params, String defaultMediaType) {
-    if (params == null) {
-      return defaultMediaType;
-    }
     final String wtParam = params.get(WT);
     if (StrUtils.isBlank(wtParam)) return defaultMediaType;
 

solr/core/src/java/org/apache/solr/handler/designer/DefaultSampleDocumentsLoader.java

@@ -78,10 +78,6 @@ public SampleDocuments parseDocsFromStream(
       return SampleDocuments.NONE;
     }
 
-    if (params == null) {
-      params = new ModifiableSolrParams();
-    }
-
     Long streamSize = stream.getSize();
     if (streamSize != null && streamSize > MAX_STREAM_SIZE) {
       throw new SolrException(

solr/core/src/java/org/apache/solr/request/SolrQueryRequest.java

@@ -75,7 +75,7 @@ static boolean disallowPartialResults(SolrParams params) {
     return !allowPartialResults(params);
   }
 
-  /** returns the current request parameters */
+  /** The parameters for this request; never null. Use {@link #setParams(SolrParams)} to change. */
   SolrParams getParams();
 
   /**
@@ -88,8 +88,8 @@ static boolean disallowPartialResults(SolrParams params) {
   Iterable<ContentStream> getContentStreams();
 
   /**
-   * Returns the original request parameters. As this does not normally include configured defaults
-   * it's more suitable for logging.
+   * The original request parameters; never null. As this does not normally include configured
+   * defaults, it's more suitable for logging.
    */
   SolrParams getOriginalParams();
 

solr/core/src/java/org/apache/solr/request/SolrQueryRequestBase.java

@@ -22,6 +22,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 import org.apache.solr.api.ApiBag;
 import org.apache.solr.common.SolrException;
 import org.apache.solr.common.params.SolrParams;
@@ -62,8 +63,8 @@ public abstract class SolrQueryRequestBase implements SolrQueryRequest, Closeabl
   public SolrQueryRequestBase(SolrCore core, SolrParams params, RTimerTree requestTimer) {
     this.core = core;
     this.schema = null == core ? null : core.getLatestSchema();
-    this.params = this.origParams = params;
-    this.requestTimer = requestTimer;
+    this.params = this.origParams = Objects.requireNonNull(params);
+    this.requestTimer = Objects.requireNonNull(requestTimer);
     this.startTime = System.currentTimeMillis();
   }
 
@@ -90,7 +91,7 @@ public SolrParams getOriginalParams() {
 
   @Override
   public void setParams(SolrParams params) {
-    this.params = params;
+    this.params = Objects.requireNonNull(params);
   }
 
   // Get the start time of this request in milliseconds

solr/core/src/java/org/apache/solr/search/QParser.java

@@ -21,6 +21,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 import org.apache.lucene.search.Query;
 import org.apache.solr.common.SolrException;
 import org.apache.solr.common.params.CommonParams;
@@ -62,10 +63,11 @@ public abstract class QParser {
   /**
    * Constructor for the QParser
    *
-   * @param qstr The part of the query string specific to this parser
-   * @param localParams The set of parameters that are specific to this QParser. See
+   * @param qstr The query string to be parsed
+   * @param localParams Params scoped to this query, customizing the parsing. Null if none. Most
+   *     params the parser needs are resolved here first, overlaying the request. See
    *     https://solr.apache.org/guide/solr/latest/query-guide/local-params.html
-   * @param params The rest of the {@link org.apache.solr.common.params.SolrParams}
+   * @param params Params for the request, taken from {@link SolrQueryRequest#getParams()}; not null
    * @param req The original {@link org.apache.solr.request.SolrQueryRequest}.
    */
   public QParser(String qstr, SolrParams localParams, SolrParams params, SolrQueryRequest req) {
@@ -97,7 +99,7 @@ public QParser(String qstr, SolrParams localParams, SolrParams params, SolrQuery
       }
     }
 
-    this.params = params;
+    this.params = Objects.requireNonNull(params);
     this.req = req;
   }
 
@@ -160,7 +162,7 @@ public SolrParams getParams() {
   }
 
   public void setParams(SolrParams params) {
-    this.params = params;
+    this.params = Objects.requireNonNull(params);
   }
 
   public SolrQueryRequest getReq() {

solr/core/src/java/org/apache/solr/search/QParserPlugin.java

@@ -95,7 +95,11 @@ public abstract class QParserPlugin implements NamedListInitializedPlugin, SolrI
     standardPlugins = Collections.unmodifiableMap(map);
   }
 
-  /** return a {@link QParser} */
+  /**
+   * Creates the {@link QParser}.
+   *
+   * @see QParser#QParser(String, SolrParams, SolrParams, SolrQueryRequest)
+   */
   public abstract QParser createParser(
       String qstr, SolrParams localParams, SolrParams params, SolrQueryRequest req);
 

solr/core/src/java/org/apache/solr/update/processor/IgnoreCommitOptimizeUpdateProcessorFactory.java

@@ -50,13 +50,13 @@ public class IgnoreCommitOptimizeUpdateProcessorFactory extends UpdateRequestPro
 
   @Override
   public void init(final NamedList<?> args) {
-    SolrParams params = (args != null) ? args.toSolrParams() : null;
-    if (params == null) {
+    if (args == null) {
       errorCode = ErrorCode.FORBIDDEN; // default is 403 error
       responseMsg = DEFAULT_RESPONSE_MSG;
       ignoreOptimizeOnly = false;
       return;
     }
+    SolrParams params = args.toSolrParams();
 
     ignoreOptimizeOnly = params.getBool("ignoreOptimizeOnly", false);
 

solr/core/src/test/org/apache/solr/cloud/LeaderFailureAfterFreshStartTest.java

@@ -38,7 +38,6 @@
 import org.apache.solr.common.SolrInputDocument;
 import org.apache.solr.common.cloud.Replica;
 import org.apache.solr.common.cloud.ZkStateReader;
-import org.apache.solr.common.params.ModifiableSolrParams;
 import org.junit.Test;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -241,8 +240,6 @@ protected void indexDoc(Object... fields) throws IOException, SolrServerExceptio
 
     UpdateRequest ureq = new UpdateRequest();
     ureq.add(doc);
-    ModifiableSolrParams params = new ModifiableSolrParams();
-    ureq.setParams(params);
     ureq.process(cloudClient);
   }
 

solr/core/src/test/org/apache/solr/cloud/PeerSyncReplicationTest.java

@@ -43,7 +43,6 @@
 import org.apache.solr.common.SolrInputDocument;
 import org.apache.solr.common.cloud.Replica;
 import org.apache.solr.common.cloud.ZkStateReader;
-import org.apache.solr.common.params.ModifiableSolrParams;
 import org.apache.solr.core.CoreContainer;
 import org.apache.solr.metrics.SolrMetricManager;
 import org.junit.Test;
@@ -369,8 +368,6 @@ protected void indexDoc(Object... fields) throws IOException, SolrServerExceptio
 
     UpdateRequest ureq = new UpdateRequest();
     ureq.add(doc);
-    ModifiableSolrParams params = new ModifiableSolrParams();
-    ureq.setParams(params);
     ureq.process(cloudClient);
   }
 

solr/core/src/test/org/apache/solr/cloud/TestStressInPlaceUpdates.java

@@ -625,11 +625,8 @@ protected long addDocAndGetVersion(Object... fields) throws Exception {
     SolrInputDocument doc = new SolrInputDocument();
     addFields(doc, fields);
 
-    ModifiableSolrParams params = new ModifiableSolrParams();
-    params.add("versions", "true");
-
     UpdateRequest ureq = new UpdateRequest();
-    ureq.setParams(params);
+    ureq.getParams().set("versions", true);
     ureq.add(doc);
     UpdateResponse resp;
 
@@ -647,10 +644,10 @@ protected long addDocAndGetVersion(Object... fields) throws Exception {
 
   protected long deleteDocAndGetVersion(
       String id, ModifiableSolrParams params, boolean deleteByQuery) throws Exception {
-    params.add("versions", "true");
-
     UpdateRequest ureq = new UpdateRequest();
-    ureq.setParams(params);
+    ureq.getParams().add(params);
+    ureq.getParams().set("versions", true);
+
     if (deleteByQuery) {
       ureq.deleteByQuery("id:" + id);
     } else {

solr/core/src/test/org/apache/solr/handler/TestSampleDocumentsLoader.java

@@ -52,7 +52,7 @@ public void setup() throws IOException {
 
   @Test
   public void testJson() throws Exception {
-    loadTestDocs(null, new File(exampleDir, "films/films.json"), 500, 500);
+    loadTestDocs(SolrParams.of(), new File(exampleDir, "films/films.json"), 500, 500);
   }
 
   @Test
@@ -78,7 +78,7 @@ public void testCsv() throws Exception {
 
   @Test
   public void testSolrXml() throws Exception {
-    loadTestDocs(null, new File(exampleDir, "films/films.xml"), 1000, 1000);
+    loadTestDocs(SolrParams.of(), new File(exampleDir, "films/films.xml"), 1000, 1000);
   }
 
   protected List<SolrInputDocument> loadTestDocs(

solr/core/src/test/org/apache/solr/handler/admin/TestApiFramework.java

@@ -250,7 +250,6 @@ public void read(SolrQueryRequest req, SolrQueryResponse rsp) {
 
   private static SolrQueryResponse v2ApiInvoke(
       ApiBag bag, String uri, String method, SolrParams params, InputStream payload) {
-    if (params == null) params = new ModifiableSolrParams();
     SolrQueryResponse rsp = new SolrQueryResponse();
     HashMap<String, String> templateVals = new HashMap<>();
     Api[] currentApi = new Api[1];

solr/core/src/test/org/apache/solr/handler/api/V2ApiUtilsTest.java

@@ -22,6 +22,7 @@
 import jakarta.ws.rs.core.MediaType;
 import org.apache.solr.SolrTestCaseJ4;
 import org.apache.solr.common.params.ModifiableSolrParams;
+import org.apache.solr.common.params.SolrParams;
 import org.junit.Test;
 
 public class V2ApiUtilsTest extends SolrTestCaseJ4 {
@@ -44,9 +45,7 @@ public void testReadsDisableV2ApiSysprop() {
 
   @Test
   public void testConvertsWtToMediaTypeString() {
-    assertEquals(
-        "someDefault",
-        V2ApiUtils.getMediaTypeFromWtParam(new ModifiableSolrParams(), "someDefault"));
+    assertEquals("someDefault", V2ApiUtils.getMediaTypeFromWtParam(SolrParams.of(), "someDefault"));
 
     var params = new ModifiableSolrParams();
     params.add("wt", "json");

solr/core/src/test/org/apache/solr/security/BaseTestRuleBasedAuthorizationPlugin.java

@@ -840,7 +840,7 @@ public MockAuthorizationContext(Map<String, Object> values) {
     @Override
     public SolrParams getParams() {
       SolrParams params = (SolrParams) values.get("params");
-      return params == null ? new MapSolrParams(new HashMap<>()) : params;
+      return params == null ? SolrParams.of() : params;
     }
 
     @Override