code: package com.google.javascript.rhino.jstype;
  
  import com.google.javascript.rhino.jstype.ObjectType;
  import com.google.common.collect.ImmutableSet;
  
  import java.util.Set;
  
  class CheckNull {
    void pattern(ObjectType interfaceType) {
      ObjectType implicitProto = interfaceType.getImplicitPrototype();
      Set<String> currentPropertyNames;
      if (implicitProto == null) {
        currentPropertyNames = ImmutableSet.of();
      } else {
        currentPropertyNames = implicitProto.getOwnPropertyNames();
      }
      for (String name : currentPropertyNames) {
        // do something with the name...
      }
    }
  }
  