Fix constraints initialization
@@ -36,6 +36,7 @@ package com.google.refine.model;
import java.io.IOException;
import java.io.Writer;
import java.lang.reflect.Method;
+import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
@@ -67,7 +68,7 @@ public class Column {
private String format = Field.FIELD_FORMAT_DEFAULT;
private String title = "";
private String description = "";
- private Map<String, Object> constraints = null;
+ private Map<String, Object> constraints = Collections.emptyMap();
transient protected Map<String, Object> _precomputes;
