The accepted answer from @arshajii is totally correct. However just being more explicit by saying below,

StringUtils.isBlank()

 StringUtils.isBlank(null)      = true
 StringUtils.isBlank("")        = true  
 StringUtils.isBlank(" ")       = true  
 StringUtils.isBlank("bob")     = false  
 StringUtils.isBlank("  bob  ") = false

StringUtils.isEmpty

 StringUtils.isEmpty(null)      = true
 StringUtils.isEmpty("")        = true  
 StringUtils.isEmpty(" ")       = false  
 StringUtils.isEmpty("bob")     = false  
 StringUtils.isEmpty("  bob  ") = false

To detect if a string is null or empty, you can use the following without including any external dependencies on your project and still keeping your code simple/clean:

if(myString==null || myString.isEmpty()){
    //do something
}

or if blank spaces need to be detected as well:

if(myString==null || myString.trim().isEmpty()){
    //do something
}

you could easily wrap these into utility methods to be more concise since these are very common checks to make:

public final class StringUtils{

    private StringUtils() { }   

    public static bool isNullOrEmpty(string s){
        if(s==null || s.isEmpty()){
            return true;
        }
        return false;
    }

    public static bool isNullOrWhiteSpace(string s){
        if(s==null || s.trim().isEmpty()){
            return true;
        }
        return false;
    }
}

and then call these methods via:

if(StringUtils.isNullOrEmpty(myString)){...}

and

if(StringUtils.isNullOrWhiteSpace(myString)){...}

You can use new String class function added since JDK11, the String.isBlank()

Docs here

isBlank
public boolean isBlank()

Returns true if the string is empty or contains only white space codepoints, otherwise false.
Since:
11

Also, as per your use-case advise to go through : StringUtils.isBlank()VsString.isEmpty()