In web development, a requirement is often encountered, which is to judge that the variable is null or empty string (""), which affects the page display logic. There are corresponding methods to judge in velocity. Of course, you can also convert it to valid values in the java backend before making judgments. The following is what I have summarized in my development, I hope it will be helpful to everyone!
(1) Judgment null
#if( $name == null)
something code
#end
(2) Judgment null or false
#if( !$name)
something code
#end
(3) Determine null or empty string
#if( "$!name" == "")
something code
#end