Error: Expected 3 outcomes but returned 0 -- why doesnt this implementation w/ helper method not work?

package com.example;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Date;
import java.util.List;

public class BlogPost implements Comparable<BlogPost>, Serializable {
  private String mAuthor;
  private String mTitle;
  private String mBody;
  private String mCategory;
  private Date mCreationDate;

  public BlogPost(String author, String title, String body, String category, Date creationDate) {
    mAuthor = author;
    mTitle = title;
    mBody = body;
    mCategory = category;
    mCreationDate = creationDate;
  }

  public int compareTo(BlogPost other) {
    if (equals(other)) {
      return 0;
    }
    return mCreationDate.compareTo(other.mCreationDate);
  }

  public String[] getWords() {
    return mBody.toLowerCase().split("\\s+");
  }

  public List<String> getExternalLinks(){
    return getWordsPrefixedWith("http");
  }

  private List<String> getWordsPrefixedWith(String prefix){
    List<String> results = new ArrayList<String>();
    for(String word : getWords()){
     if(word.startsWith("prefix")){  //should this be in quotes?? Just call String prefix direct?
       results.add(word);
      }
    }
    return results;
  } 

}