fix(aggregate-operation): move type assertions to constructor

lib/operations/aggregate.js

@@ -38,6 +38,16 @@ class AggregateOperation extends CommandOperationV2 {
     if (this.hasWriteStage) {
       this.readPreference = ReadPreference.primary;
     }
+
+    if (options.explain && (this.readConcern || this.writeConcern)) {
+      throw new MongoError(
+        '"explain" cannot be used on an aggregate call with readConcern/writeConcern'
+      );
+    }
+
+    if (options.cursor != null && typeof options.cursor !== 'object') {
+      throw new MongoError('cursor options must be an object');
+    }
   }
 
   get canRetryRead() {
@@ -52,6 +62,7 @@ class AggregateOperation extends CommandOperationV2 {
     const command = { aggregate: this.target, pipeline: this.pipeline };
 
     if (
+      this.readConcern &&
       (!this.hasWriteStage || serverWireVersion >= MIN_WIRE_VERSION_$OUT_READ_CONCERN_SUPPORT) &&
       !inTransaction
     ) {
@@ -85,29 +96,13 @@ class AggregateOperation extends CommandOperationV2 {
     }
 
     if (options.explain) {
-      if (command.readConcern || command.writeConcern) {
-        callback(
-          new MongoError(
-            '"explain" cannot be used on an aggregate call with readConcern/writeConcern'
-          )
-        );
-
-        return;
-      }
-
       command.explain = options.explain;
     }
 
     if (typeof options.comment === 'string') {
       command.comment = options.comment;
     }
 
-    // Validate that cursor options is valid
-    if (options.cursor != null && typeof options.cursor !== 'object') {
-      callback(new MongoError('cursor options must be an object'));
-      return;
-    }
-
     command.cursor = options.cursor || {};
     if (options.batchSize && !this.hasWriteStage) {
       command.cursor.batchSize = options.batchSize;