title: Condition not satisfied when comparing empty Strings in Spock
body: <p>I'm trying to check that 2 strings are equal but I'm hitting. Both Strings are empty:</p>
  
  <pre><code>Condition not satisfied:
  
  versionTagPrefix == ""
  |                |
  ""               false
                   2 differences (0% similarity)
                   ("")
                   (--)
  </code></pre>
  
  <p>I've also tried equals:</p>
  
  <pre><code>Condition not satisfied:
  
  "".equals(versionTagPrefix)
     |      |
     false  ""
  </code></pre>
  
  <p>Versions:</p>
  
  <pre><code>compile 'org.codehaus.groovy:groovy-all:2.0.1'
  testCompile "org.spockframework:spock-core:0.7-groovy-2.0"
  </code></pre>