diff --git a/java/com/android/dialer/app/calllog/calllogcache/CallLogCache.java b/java/com/android/dialer/app/calllog/calllogcache/CallLogCache.java
index 514fda5..2e7c933 100644
--- a/java/com/android/dialer/app/calllog/calllogcache/CallLogCache.java
+++ b/java/com/android/dialer/app/calllog/calllogcache/CallLogCache.java
@@ -17,6 +17,7 @@
 package com.android.dialer.app.calllog.calllogcache;
 
 import android.content.Context;
+import android.support.annotation.Nullable;
 import android.telecom.PhoneAccountHandle;
 import com.android.dialer.app.calllog.CallLogAdapter;
 import com.android.dialer.util.CallUtil;
@@ -57,7 +58,8 @@
    * Returns true if the given number is the number of the configured voicemail. To be able to
    * mock-out this, it is not a static method.
    */
-  public abstract boolean isVoicemailNumber(PhoneAccountHandle accountHandle, CharSequence number);
+  public abstract boolean isVoicemailNumber(
+      PhoneAccountHandle accountHandle, @Nullable CharSequence number);
 
   /**
    * Returns {@code true} when the current sim supports checking video calling capabilities via the
diff --git a/java/com/android/dialer/app/calllog/calllogcache/CallLogCacheLollipopMr1.java b/java/com/android/dialer/app/calllog/calllogcache/CallLogCacheLollipopMr1.java
index f856806..2424b6d 100644
--- a/java/com/android/dialer/app/calllog/calllogcache/CallLogCacheLollipopMr1.java
+++ b/java/com/android/dialer/app/calllog/calllogcache/CallLogCacheLollipopMr1.java
@@ -17,7 +17,9 @@
 package com.android.dialer.app.calllog.calllogcache;
 
 import android.content.Context;
+import android.support.annotation.Nullable;
 import android.telecom.PhoneAccountHandle;
+import android.text.TextUtils;
 import android.util.ArrayMap;
 import com.android.dialer.calllogutils.PhoneAccountUtils;
 import com.android.dialer.telecom.TelecomUtil;
@@ -50,7 +52,11 @@
   }
 
   @Override
-  public boolean isVoicemailNumber(PhoneAccountHandle accountHandle, CharSequence number) {
+  public boolean isVoicemailNumber(
+      PhoneAccountHandle accountHandle, @Nullable CharSequence number) {
+    if (TextUtils.isEmpty(number)) {
+      return false;
+    }
     return TelecomUtil.isVoicemailNumber(mContext, accountHandle, number.toString());
   }