code: @Nonnull
    public JSConditional _if (@Nonnull final IJSExpression aTest, @Nullable final IHasJSCode aThen)
    {
      return addStatement (new JSConditional (aTest, aThen));
    }
docs: Create an If statement and add it to this block
  
  @param aTest
  {@link IJSExpression} to be tested to determine branching
  @param aThen
  "then" block content. May be <code>null</code>.
  @return Newly generated conditional statement