liquibase-core/src/main/java/liquibase/precondition/PreconditionFactory.java
public Precondition create(String tagName) {
        Class<?> aClass = preconditions.get(tagName);
        if (aClass == null) {
            return null;
        }
        try {
            return (Precondition) aClass.getConstructor().newInstance();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
public Precondition create(String tagName) {
        Class<?> aClass = preconditions.get(tagName);
        if (aClass == null) {
            return null;
        }
        try {
            return (Precondition) aClass.getConstructor().newInstance();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
Create a new Precondition subclass based on the given tag name.