title: PHP array_merge not working
body: <p>Working with PHP.
  I have array 1 with this keys and values:</p>
  
  <pre><code>$array_1 = array(
  (more values)
  'propub_cost_max' =&gt; 5,
  'propub_cost_min' =&gt; 0.5,
  'average_calc_last' =&gt; '-1 Months',
  'propub_qtd_first_offer' =&gt; 4
  );
  </code></pre>
  
  <p>and array 2:</p>
  
  <pre><code>$array_2 = array(
  'propub_cost_max' =&gt; 20,
  'propub_cost_min' =&gt; (no value),
  'average_calc_last' =&gt; (no value),
  'propub_qtd_first_offer' =&gt; (no value)
  );
  </code></pre>
  
  <p>I want to merge array 2 with array 1 so i did:</p>
  
  <pre><code>$result = array_merge($array_2, $array_1);
  </code></pre>
  
  <p>But the result is:</p>
  
  <pre><code>$result = array(
  (more values)
  'propub_cost_max' =&gt; 5,
  'propub_cost_min' =&gt; 0.5,
  'average_calc_last' =&gt; '-1 Months',
  'propub_qtd_first_offer' =&gt; 4
  );
  </code></pre>
  
  <p>The propub_cost_max key should assume the value 20, right?</p>
  
  <p>The idea is to maintain some values, and replace where the values are different if there is any value, of course.
  I thought that array_merge should work, but...</p>
  
  <p>Thank you all.</p>