NetworkTable.containsKey(): Always return false on empty key.

src/main/java/edu/wpi/first/networktables/NetworkTable.java

@@ -156,7 +156,7 @@ public final class NetworkTable {
    * @return true if the table as a value assigned to the given key
    */
   public boolean containsKey(String key) {
-    return getEntry(key).exists();
+    return !("".equals(key)) && getEntry(key).exists();
   }
 
   /**

src/main/native/cpp/networktables/NetworkTable.cpp

@@ -286,7 +286,7 @@ std::shared_ptr<NetworkTable> NetworkTable::GetSubTable(StringRef key) const {
 }
 
 bool NetworkTable::ContainsKey(StringRef key) const {
-  return GetEntry(key).Exists();
+  return !key.empty() && GetEntry(key).Exists();
 }
 
 bool NetworkTable::ContainsSubTable(StringRef key) const {