return null defaultValue for complex default expressions

Author: imor

docs/changelog.md

@@ -84,5 +84,5 @@
 ## 1.5.6
 - feature: add support for filtering on array column types using `contains`, `containedBy`, `overlaps`, `is`, `eq`
 
-
 ## master
+- bugfix: UDF argument with a complex default expression was marked as required

src/sql_types.rs

@@ -294,7 +294,7 @@ impl<'a> ArgsIterator<'a> {
         if res.is_some() {
             res
         } else {
-            Some(DefaultValue::NonNull(trimmed.to_string()))
+            Some(DefaultValue::Null)
         }
     }
 }

test/expected/issue_533.out

@@ -52,7 +52,7 @@ begin;
                                      "name": "UUID",                   +
                                      "ofType": null                    +
                                  },                                    +
-                                 "defaultValue": "uid()"               +
+                                 "defaultValue": null                  +
                              }                                         +
                          ],                                            +
                          "name": "getUserId",                          +
@@ -181,7 +181,7 @@ begin;
                                      "name": "String",                 +
                                      "ofType": null                    +
                                  },                                    +
-                                 "defaultValue": "uid()"               +
+                                 "defaultValue": null                  +
                              }                                         +
                          ],                                            +
                          "name": "getUserId",                          +
@@ -305,7 +305,7 @@ begin;
                                      "name": "Int",                    +
                                      "ofType": null                    +
                                  },                                    +
-                                 "defaultValue": "(1 + 1)"             +
+                                 "defaultValue": null                  +
                              },                                        +
                              {                                         +
                                  "name": "b",                          +
@@ -314,7 +314,7 @@ begin;
                                      "name": "Int",                    +
                                      "ofType": null                    +
                                  },                                    +
-                                 "defaultValue": "(2 + 2)"             +
+                                 "defaultValue": null                  +
                              }                                         +
                          ],                                            +
                          "name": "addNums",                            +