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package liquibase.util;

import liquibase.ExtensibleObject;

import java.security.SecureRandom;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.TreeSet;
import java.util.regex.Pattern;

/**
 * Various utility methods for working with strings.
 */
public class StringUtil {
    private static final Pattern upperCasePattern = Pattern.compile(".*[A-Z].*");
    private static final Pattern lowerCasePattern = Pattern.compile(".*[a-z].*");
    private static final SecureRandom rnd = new SecureRandom();
    /**
     * Returns the trimmed (left and right) form of the input string. If the string is empty after trimming (or null
     * was passed in the first place), null is returned, i.e. the input string is reduced to nothing.
     * @param string the string to trim
     * @return the trimmed string or null
     */
import java.util.regex.Pattern;

/**
 * Various utility methods for working with strings.
 */
public class StringUtil {
... 
    public static String trimToNull(String string) {
        if (string == null) {
            return null;
        }
        String returnString = string.trim();
        if (returnString.isEmpty()) {
            return null;
        } else {
            return returnString;
        }
    }
...
}