diff --git a/pgloader.asd b/pgloader.asd
index 0ab7010..f2b55df 100644
--- a/pgloader.asd
+++ b/pgloader.asd
@@ -76,6 +76,10 @@
                                                        "report"))
                          (:file "archive" :depends-on ("logs"))
 
+                         (:file "pg-format-column" :depends-on ("schema-structs"
+                                                                "monitor"
+                                                                "state"))
+
                          ;; generic connection api
                          (:file "connection" :depends-on ("archive"))))
 
diff --git a/src/package.lisp b/src/package.lisp
index 4642838..4219148 100644
--- a/src/package.lisp
+++ b/src/package.lisp
@@ -68,7 +68,7 @@
            #:column-name
            #:column-type-name
            #:column-type-mod
-           #:column-type-nullable
+           #:column-nullable
            #:column-default
            #:column-comment
            #:column-transform
@@ -99,9 +99,7 @@
            #:push-to-end
            #:with-schema
 
-           #:format-table-name
-           #:format-default-value
-           #:format-column))
+           #:format-table-name))
 
 (defpackage #:pgloader.state
   (:use #:cl #:pgloader.params #:pgloader.schema)
diff --git a/src/utils/pg-format-column.lisp b/src/utils/pg-format-column.lisp
new file mode 100644
index 0000000..ad371b9
--- /dev/null
+++ b/src/utils/pg-format-column.lisp
@@ -0,0 +1,40 @@
+;;;
+;;; PostgreSQL column and type output
+;;;
+
+(in-package #:pgloader.utils)
+
+(defun format-default-value (default &optional transform)
+  "Returns suitably quoted default value for CREATE TABLE command."
+  (cond
+    ((null default) "NULL")
+    ((and (stringp default) (string= "NULL" default)) default)
+    ((and (stringp default) (string= "CURRENT_TIMESTAMP" default)) default)
+    ((and (stringp default) (string= "CURRENT TIMESTAMP" default))
+     "CURRENT_TIMESTAMP")
+    ((and (stringp default) (string= "newsequentialid()" default))
+     "uuid_generate_v1()")
+    (t
+     ;; apply the transformation function to the default value
+     (if transform (format-default-value
+                    (handler-case
+                        (funcall transform default)
+                      (condition (c)
+                        (log-message :warning
+                                     "Failed to transform default value ~s: ~a"
+                                     default c)
+                        ;; can't transform: return nil
+                        nil)))
+	 (format nil "'~a'" default)))))
+
+(defmethod format-column ((column column))
+  "Format the PostgreSQL data type."
+  (format nil
+          "~a ~22t ~a~:[~*~;~a~]~:[ not null~;~]~:[~; default ~a~]"
+          (column-name column)
+          (column-type-name column)
+          (column-type-mod column)
+          (column-type-mod column)
+          (column-nullable column)
+          (column-default column)
+          (column-default column)))
diff --git a/src/utils/schema-structs.lisp b/src/utils/schema-structs.lisp
index 6eac209..d05c02e 100644
--- a/src/utils/schema-structs.lisp
+++ b/src/utils/schema-structs.lisp
@@ -347,35 +347,3 @@
                       (cdr ,table-name)))
             (string ,table-name))))
      ,@body))
-
-
-
-;;;
-;;; PostgreSQL column and type output
-;;;
-(defun format-default-value (default &optional transform)
-  "Returns suitably quoted default value for CREATE TABLE command."
-  (cond
-    ((null default) "NULL")
-    ((and (stringp default) (string= "NULL" default)) default)
-    ((and (stringp default) (string= "CURRENT_TIMESTAMP" default)) default)
-    ((and (stringp default) (string= "CURRENT TIMESTAMP" default))
-     "CURRENT_TIMESTAMP")
-    ((and (stringp default) (string= "newsequentialid()" default))
-     "uuid_generate_v1()")
-    (t
-     ;; apply the transformation function to the default value
-     (if transform (format-default-value (funcall transform default))
-	 (format nil "'~a'" default)))))
-
-(defmethod format-column ((column column))
-  "Format the PostgreSQL data type."
-  (with-slots (name type-name type-mod nullable default transform) column
-    (format nil
-            "~a ~22t ~a~:[~*~;~a~]~:[ not null~;~]~:[~; default ~a~]"
-            name
-            type-name
-            type-mod
-            type-mod
-            nullable
-            default default)))
diff --git a/src/utils/transforms.lisp b/src/utils/transforms.lisp
index 4e33e66..757cded 100644
--- a/src/utils/transforms.lisp
+++ b/src/utils/transforms.lisp
@@ -226,7 +226,9 @@
   (declare (type (or null string (simple-array (unsigned-byte 8) (*))) vector))
   (etypecase vector
     (null nil)
-    (string (assert (string= "" vector)) nil)
+    (string (if (string= "" vector)
+                nil
+                (error "byte-vector-to-bytea called on a string: ~s" vector)))
     (simple-array
      (let ((hex-digits "0123456789abcdef")
            (bytea (make-array (+ 2 (* 2 (length vector)))