Only set marker on children who can have a marker as their anchor, fixing type checks too

Author: SpangleLabs

packages/react-google-maps-api/src/components/drawing/Marker.tsx

@@ -249,11 +249,20 @@ export class Marker extends React.PureComponent<MarkerProps, MarkerState> {
   }
 
   render(): React.ReactNode {
-    let children: ReactNode[]|null = null
+    interface HasMarkerAnchor {
+      anchor?: google.maps.Marker | null
+    }
+
+    let children: ReactNode | null = null
     if(this.props.children) {
-      children = React.Children.toArray(this.props.children).map(
-        (e) => {return React.cloneElement(e, {anchor: this.state.marker})}
-      )
+      children = React.Children.map(this.props.children, child => {
+        if(!React.isValidElement<HasMarkerAnchor>(child)) {
+          return child;
+        }
+
+        let elementChild: React.ReactElement<HasMarkerAnchor> = child;
+        return React.cloneElement(elementChild, {anchor: this.state.marker});
+      })
     }
     return children || null
   }