Also clarify SolrRequest.getParams nad QParser params

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/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/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