CodeQL documentation

Container contents are never initialized

ID: java/empty-container
Kind: problem
Severity: error
Precision: very-high
   - reliability
   - maintainability
   - useless-code
   - external/cwe/cwe-561
Query suites:
   - java-security-and-quality.qls

Click to see the query in the CodeQL repository

A method that queries the contents of a collection or map (such as containsKey or isEmpty) is invoked on an object that is known to be empty. Such method calls do not return interesting results, and may indicate missing code or a logic error.


Either remove the collection/map if it is unnecessary, or ensure that it contains the elements it was meant to contain.


The following example code iterates over an array of objects to determine whether it contains duplicate elements. It maintains a collection seen, which is intended to contain all the elements seen so far in traversing the array. If the current element is already contained in that collection then the method returns true, indicating that a duplicate has been found.

Note, however, that no elements are ever actually added to seen, so the method always returns false.

boolean containsDuplicates(Object[] array) {
	java.util.Set<Object> seen = new java.util.HashSet<Object>();
	for (Object o : array) {
		if (seen.contains(o))
			return true;
	return false;

To fix this problem, a statement seen.add(o); should be added to the end of the loop body to ensure that seen is correctly maintained.