refactor(material/select): removed the redundant initializer in select file (#27555)

(cherry picked from commit 7c88bce)

Author: alkavats1

src/material/select/select.ts

@@ -1297,7 +1297,7 @@ export class MatSelect
 
   /** Emits change event to set the model value. */
   private _propagateChanges(fallbackValue?: any): void {
-    let valueToEmit: any = null;
+    let valueToEmit: any;
 
     if (this.multiple) {
       valueToEmit = (this.selected as MatOption[]).map(option => option.value);