StringUtils.isBlank() checks that each character of the string is a whitespace character (or that the string is empty or that it's null). This is totally different than just checking if the string is empty.

From the linked documentation:

Checks if a String is whitespace, empty ("") or null.

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

For comparison StringUtils.isEmpty:

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

Warning: In java.lang.String.isBlank() and java.lang.String.isEmpty() work the same except they don't return true for null.

java.lang.String.isBlank() (since Java 11)

java.lang.String.isEmpty()

No, absolutely not - because if acct is null, it won't even get to isEmpty... it will immediately throw a NullPointerException.

Your test should be:

if (acct != null && !acct.isEmpty())

Note the use of && here, rather than your || in the previous code; also note how in your previous code, your conditions were wrong anyway - even with && you would only have entered the if body if acct was an empty string.

Alternatively, using Guava:

if (!Strings.isNullOrEmpty(acct))

Of course not. Do you really think "" is not clear enough ?

Constants have essentially 3 use cases:

1. Document the meaning of a value (with constant name + javadoc)
2. Synchronize clients on a common value.
3. Provide a shortcut to a special value to avoid some init costs

None apply here.

Correct way to check for null or empty or string containing only spaces is like this:

if(str != null && !str.trim().isEmpty()) { /* do your stuffs here */ }