javagit/src/main/java/edu/nyu/cs/javagit/utilities/CheckUtilities.java
public static void validateListRefType(List<Ref> list, Ref.RefType type, String variableName) {
    // TODO (ns1344): Write a unit test for this method.
    checkNullListArgument(list, variableName);
    for (Ref ref : list) {
      validateArgumentRefType(ref, type, variableName);
    }
  }
public static void validateListRefType(List<Ref> list, Ref.RefType type, String variableName) {
    // TODO (ns1344): Write a unit test for this method.
    checkNullListArgument(list, variableName);
    for (Ref ref : list) {
      validateArgumentRefType(ref, type, variableName);
    }
  }
Checks a <code>List</code> argument to make sure that all the <code>Ref</code> in the list
are of same <code>refType</code> type. If there is a mismatch
<code>IllegalArgumentException</code> is thrown.

@param list
The <code>List</code> to check.
@param type
The <code>refType</code> check against.
@param variableName
The name of the variable being checked; for use in exception messages.