public final BooleanExpression containsKey(K key) {
        return Expressions.booleanOperation(Ops.CONTAINS_KEY, mixin, ConstantImpl.create(key));
    }
Create a {@code key in keys(this)} expression

@param key key
@return expression
querydsl-core/src/main/java/com/querydsl/core/types/dsl/MapExpressionBase.java