Function adding body class to custom post type breaks GP generated body classes

Hi,
Weird problem and I'm hoping you can help! I added a custom function (via functions.php in a GP child theme) to dynamically add a body class based on a custom post type taxonomy. The purpose: I'm using the Modern Events Calendar and I want to mark the Events tab (and its event-related children) as "current" or "ancestor" - and remove the "current" styling on the blog tab . The following function works great:

function custom_body_classes( $classes ) {
if ( is_single() ) {
global $post;
foreach ( ( get_the_terms( $post->ID, 'mec_category' ) ) as $term) { 
$classes[] = $term->slug;
}
}
return $classes;
}
add_filter( 'body_class', 'custom_body_classes' );

BUT as soon as I load a non-Event page on the front end, this PHP error is being generated:
Invalid argument supplied for foreach()

THIS modification to the custom function works & resolves the error BUT it's interfering with the GP generated body classes:

function custom_body_classes( $classes ) {
if ( is_single() ) {
global $post;
$my_terms = get_the_terms( $post->ID, 'mec_category' ); 
if ( $my_terms && ! is_wp_error( $my_terms ) ) {
foreach ( $my_terms as $term ) {
$classes[] = $term->slug;
}
}
return $classes;
}
}
add_filter( 'body_class', 'custom_body_classes' );

This is the list of body classes for the blog when the first custom function is in place:
blog logged-in wp-custom-logo wp-embed-responsive post-image-below-header post-image-aligned-center slideout-enabled slideout-mobile sticky-menu-fade right-sidebar nav-float-right one-container nav-search-enabled header-aligned-right dropdown-hover

And this is the list of body classes for the blog when the second / revised function is on place:
right-sidebar nav-float-right one-container nav-search-enabled header-aligned-right dropdown-hover

Any thoughts about why this is happening and suggestions for tweaking the function so it doesn't bork the GP generated classes?

Thanks!
pk