Use a new version of Preconditions.checkNotNull() to avoid String computations on the happy path

Author: dconeybe

firebase-firestore/src/main/java/com/google/firebase/firestore/local/MemoryDocumentOverlayCache.java

@@ -71,7 +71,7 @@ private void saveOverlay(int largestBatchId, Mutation mutation) {
   @Override
   public void saveOverlays(int largestBatchId, Map<DocumentKey, Mutation> overlays) {
     for (Map.Entry<DocumentKey, Mutation> entry : overlays.entrySet()) {
-      Mutation overlay = checkNotNull(entry.getValue(), "null value for key: " + entry.getKey());
+      Mutation overlay = checkNotNull(entry.getValue(), "null value for key: %s", entry.getKey());
       saveOverlay(largestBatchId, overlay);
     }
   }

firebase-firestore/src/main/java/com/google/firebase/firestore/local/SQLiteDocumentOverlayCache.java

@@ -127,7 +127,7 @@ private void saveOverlay(int largestBatchId, DocumentKey key, Mutation mutation)
   public void saveOverlays(int largestBatchId, Map<DocumentKey, Mutation> overlays) {
     for (Map.Entry<DocumentKey, Mutation> entry : overlays.entrySet()) {
       DocumentKey key = entry.getKey();
-      Mutation overlay = checkNotNull(entry.getValue(), "null value for key: " + key);
+      Mutation overlay = checkNotNull(entry.getValue(), "null value for key: %s", key);
       saveOverlay(largestBatchId, key, overlay);
     }
   }

firebase-firestore/src/main/java/com/google/firebase/firestore/util/Preconditions.java

@@ -14,6 +14,7 @@
 
 package com.google.firebase.firestore.util;
 
+import java.util.Locale;
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
@@ -149,6 +150,24 @@ public static <T extends Object> T checkNotNull(
     return reference;
   }
 
+  /**
+   * Ensures that an object reference passed as a parameter to the calling method is not null.
+   *
+   * @param reference an object reference
+   * @param errorFormatString the exception message to use if the check fails; will be formatted
+   *     using {@link String#format}.
+   * @param formatArgs the args to specify when formatting the given {@code errorFormatString}.
+   * @return the non-null reference that was validated
+   * @throws NullPointerException if {@code reference} is null
+   */
+  public static <T extends Object> T checkNotNull(
+      @Nonnull T reference, String errorFormatString, @Nullable Object... formatArgs) {
+    if (reference == null) {
+      throw new NullPointerException(String.format(Locale.US, errorFormatString, formatArgs));
+    }
+    return reference;
+  }
+
   /**
    * Ensures the truth of an expression involving the state of the calling instance, but not
    * involving any parameters to the calling method.