public ComparableExpression<T> getValue() {
        if (value == null) {
            value = Expressions.comparableOperation(getType(), Ops.COALESCE, getExpressionList());
        }
        return value;
    }
{@code Coalesce} defines a coalesce function invocation. The coalesce function
returns null if all arguments are null and the first non-null argument
otherwise

<p>Coalesce doesn't provide the full interface for comparable expressions. To get an immutable
copy with the full expressiveness of Comparable expressions, call getValue().</p>

@author tiwe

@param <T> expression type
querydsl-core/src/main/java/com/querydsl/core/types/dsl/Coalesce.java