title: Add or update an edge in Gremlin
body: <p>I have a graph database in Azure CosmoDB that stores how similar vertices are and the edge contains the numeric value of how similar they are.</p>
  
  <p>The complication is that I want to add an edge or update by incrementing the similarity value. This is the current code I have for adding:</p>
  
  <pre><code>g.V('A').addE('similar').to(g.V('B')).property('x', 10)
  </code></pre>
  
  <p>I need something that will increase X if the edge exists, or create it if not. Pseudo code exemplifying it:</p>
  
  <pre><code>g.V('A').updateE('similar').to(g.V('B')).property('x', currentValue+2).ifNulll({g.V('A').addE('similar').to(g.V('B')).property('x', 10)})
  </code></pre>
  
  <p>is there an easy way to achieve this ?</p>