code: private void yieldConnection(CodeBuilder b, LocalVariable capVar, LocalVariable conVar) {
          if (conVar != null) {
              b.loadLocal(capVar);
              b.loadLocal(conVar);
              b.invokeInterface(TypeDesc.forClass(JDBCConnectionCapability.class),
                                "yieldConnection", null,
                                new TypeDesc[] {TypeDesc.forClass(Connection.class)});
          }
      }
docs: Generates code which emulates this:
  
  // May throw FetchException
  JDBCConnectionCapability.yieldConnection(con);
  
  @param capVar required reference to JDBCConnectionCapability
  @param conVar optional connection to yield