diff --git a/modules/app/src/main/java/org/locationtech/jtstest/function/CoverageFunctions.java b/modules/app/src/main/java/org/locationtech/jtstest/function/CoverageFunctions.java
index 7dcc957ef3..74f52f6a1b 100644
--- a/modules/app/src/main/java/org/locationtech/jtstest/function/CoverageFunctions.java
+++ b/modules/app/src/main/java/org/locationtech/jtstest/function/CoverageFunctions.java
@@ -34,16 +34,16 @@ public static Geometry validatePolygonWithGaps(Geometry geom, Geometry adjacentP
     return CoveragePolygonValidator.validate(geom, toGeometryArray(adjacentPolys), gapWidth);
   }
   
-  public static Geometry validateCoverage(Geometry geom) {
+  public static Geometry validate(Geometry geom) {
     Geometry[] invalid = CoverageValidator.validate(toGeometryArray(geom));
-    return FunctionsUtil.buildGeometry(invalid);
+    return FunctionsUtil.buildGeometryCollection(invalid, geom.getFactory().createLineString());
   }
 
-  public static Geometry validateCoverageWithGaps(Geometry geom, 
+  public static Geometry validateWithGaps(Geometry geom, 
       @Metadata(title="Gap width")
       double gapWidth) {
     Geometry[] invalid = CoverageValidator.validate(toGeometryArray(geom), gapWidth);
-    return FunctionsUtil.buildGeometry(invalid);
+    return FunctionsUtil.buildGeometryCollection(invalid, geom.getFactory().createLineString());
   }
 
   public static Geometry findGaps(Geometry geom, 
@@ -53,7 +53,7 @@ public static Geometry findGaps(Geometry geom,
   }
 
   @Metadata(description="Fast Union of a coverage")
-  public static Geometry unionCoverage(Geometry coverage) {
+  public static Geometry union(Geometry coverage) {
     Geometry[] cov = toGeometryArray(coverage);
     return CoverageUnion.union(cov);
   }
diff --git a/modules/app/src/main/java/org/locationtech/jtstest/function/FunctionsUtil.java b/modules/app/src/main/java/org/locationtech/jtstest/function/FunctionsUtil.java
index f4ee726b45..3c331308e7 100644
--- a/modules/app/src/main/java/org/locationtech/jtstest/function/FunctionsUtil.java
+++ b/modules/app/src/main/java/org/locationtech/jtstest/function/FunctionsUtil.java
@@ -79,10 +79,7 @@ public static Geometry buildGeometry(List geoms, Geometry parentGeom)
   
   public static Geometry buildGeometry(Geometry[] geoms)
   {
-    GeometryFactory gf = JTSTestBuilder.getGeometryFactory();
-    if (geoms.length > 0) {
-      gf = getFactoryOrDefault(geoms[0]);
-    }
+    GeometryFactory gf = getFactory(geoms);
     
     List<Geometry> geomList = new ArrayList<Geometry>();
     for (Geometry geom : geoms) {
@@ -95,6 +92,28 @@ public static Geometry buildGeometry(Geometry[] geoms)
     return gf.buildGeometry(geomList);
   }
   
+  public static Geometry buildGeometryCollection(Geometry[] geoms, Geometry nullGeom)
+  {
+    GeometryFactory gf = getFactory(geoms);
+    
+    Geometry[] geomArray = new Geometry[geoms.length];
+    for (int i = 0; i < geoms.length; i++) {
+      Geometry srcGeom = geoms[i] == null ? nullGeom : geoms[i];
+      if (srcGeom != null) {
+        geomArray[i] = srcGeom.copy();
+      }
+    }
+    return gf.createGeometryCollection(geomArray);
+  }
+
+  private static GeometryFactory getFactory(Geometry[] geoms) {
+    GeometryFactory gf = JTSTestBuilder.getGeometryFactory();
+    if (geoms.length > 0) {
+      gf = getFactoryOrDefault(geoms[0]);
+    }
+    return gf;
+  }
+  
   public static Geometry buildGeometry(Geometry a, Geometry b) {
     Geometry[] geoms = toGeometryArray(a, b);
     return getFactoryOrDefault(a, b).createGeometryCollection(geoms);  }