diff --git a/src/java/com/samskivert/depot/util/RuntimeUtil.java b/src/java/com/samskivert/depot/util/RuntimeUtil.java
index 91a484f..a465180 100644
--- a/src/java/com/samskivert/depot/util/RuntimeUtil.java
+++ b/src/java/com/samskivert/depot/util/RuntimeUtil.java
@@ -69,8 +69,8 @@ public class RuntimeUtil
     /**
      * Creates a function that creates an instance of R and initializes all accessible (ie. public)
      * fields of R from fields of P with matching name. If the function is applied to null, null
-     * will be returned. Fields of P that do not exist in R will be ignored and vice versa. See the
-     * class documentation for a list of field conversions that will be made automatically and the
+     * will be returned. Fields of P that do not exist in R will be ignored. See the class
+     * documentation for a list of field conversions that will be made automatically and the
      * mechanism for performing other conversions.
      */
     public static <P extends PersistentRecord, R> Function<P, R> makeToRuntime (
@@ -86,9 +86,7 @@ public class RuntimeUtil
                 try {
                     R object = rclass.newInstance();
                     for (int ii = 0, ll = rfields.length; ii < ll; ii++) {
-                        if (getters[ii] != null) {
-                            rfields[ii].set(object, getters[ii].get(record));
-                        }
+                        rfields[ii].set(object, getters[ii].get(record));
                     }
                     return object;
                 } catch (Exception e) {
@@ -118,9 +116,7 @@ public class RuntimeUtil
                 try {
                     P record = pclass.newInstance();
                     for (int ii = 0, ll = rfields.length; ii < ll; ii++) {
-                        if (setters[ii] != null) {
-                            setters[ii].set(record, rfields[ii].get(object));
-                        }
+                        setters[ii].set(record, rfields[ii].get(object));
                     }
                     return record;
                 } catch (Exception e) {
@@ -181,7 +177,10 @@ public class RuntimeUtil
 
         // if we have no persistent field for the runtime field, we're now out of luck
         if (pfield == null) {
-            return null;
+            throw new IllegalArgumentException(
+                "Cannot create mapping for " + rfield + ". Neither " +
+                pclass.getSimpleName() + "." + rfield.getName() + " nor " +
+                rfield.getType() + " " + getter + "() exist.");
         }
 
         // if the fields match exactly, return a getter that just gets the field
@@ -204,7 +203,7 @@ public class RuntimeUtil
         }
 
         // if we have exhausted all other approaches, we're SOL
-        return null;
+        throw new IllegalArgumentException("Cannot map " + pfield + " to " + rfield + ".");
     }
 
     protected static Setter makeSetter (Class<?> pclass, final Field pfield, Field rfield)
@@ -224,7 +223,8 @@ public class RuntimeUtil
 
         // if we have no persistent field for this runtime field, we're now out of luck
         if (pfield == null) {
-            return null;
+            throw new IllegalArgumentException("Cannot create setter for " + rfield + ". " +
+                                               "No corresponding field exists in " + pclass + ".");
         }
 
         // if the fields match exactly, return a setter that just sets the field
@@ -247,7 +247,7 @@ public class RuntimeUtil
         }
 
         // if we have exhausted all other approaches, we're SOL
-        return null;
+        throw new IllegalArgumentException("Cannot map " + rfield + " to " + pfield + ".");
     }
 
     protected static Field[] getPersistentFields (Class<?> pclass, Field[] rfields)