Need to check empty not null for String

getWcdmaLevel needs to check empty string, which is currently doesn't
because mWcdmaDefaultSignalMeasurement could be not null but empty string.

Test: TelephonybaseTest

Change-Id: If00a5953eef972250266ceef234cce213d45bc6a
Signed-off-by: Seongho Kim <sh_tiger.kim@samsung.com>
diff --git a/telephony/java/android/telephony/SignalStrength.java b/telephony/java/android/telephony/SignalStrength.java
index ed758a9..fb801b2 100644
--- a/telephony/java/android/telephony/SignalStrength.java
+++ b/telephony/java/android/telephony/SignalStrength.java
@@ -21,8 +21,8 @@
 import android.os.Parcel;
 import android.os.Parcelable;
 import android.telephony.CarrierConfigManager;
+import android.text.TextUtils;
 import android.util.Log;
-import android.content.res.Resources;
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -1116,7 +1116,7 @@
     public int getWcdmaLevel() {
         int level = SIGNAL_STRENGTH_NONE_OR_UNKNOWN;
 
-        if (mWcdmaDefaultSignalMeasurement == null) {
+        if (TextUtils.isEmpty(mWcdmaDefaultSignalMeasurement)) {
             Log.wtf(LOG_TAG, "getWcdmaLevel - WCDMA default signal measurement is invalid.");
             return level;
         }