code: protected String getGeneSymbol(ProteinReference pr)
  	{
  		for (Xref xr : pr.getXref())
  		{
  			String db = xr.getDb();
  			if (db != null)
  			{
  				db = db.toLowerCase();
  				if (db.startsWith("hgnc"))
  				{
  					String id = xr.getId();
  					if (id != null)
  					{
  						String symbol = HGNC.getSymbol(id);
  						if (symbol != null && !symbol.isEmpty())
  						{
  							return symbol;
  						}
  					}
  				}
  			}
  		}
  
  		return null;
  	}
docs: Searches for the gene symbol of the given EntityReference.
  @param pr to search for a symbol
  @return symbol